זמנים
הלכות עירובין
פרק ה

Halacha

הלכה א
אַנְּשֵׁי מָבוֹי שֶׁהָיָה בֵּינֵיהֶן שִׁתּוּף בְּמַאֲכָל אֶחָד לְעִנְיַן סְחוֹרָה כְּגוֹן שֶׁקָּנוּ יַיִן בְּשֻׁתָּפוּת אוֹ שֶׁמֶן אוֹ דְּבַשׁ וְכַיּוֹצֵא בָּהֶן אֵינָן צְרִיכִין שִׁתּוּף אַחֵר לְעִנְיַן שַׁבָּת אֶלָּא סוֹמְכִין עַל שִׁתּוּף שֶׁל סְחוֹרָה. וְהוּא שֶׁיִּהְיֶה הַמִּין שֶׁהֵן שֻׁתָּפִין בּוֹ מִין אֶחָד וּבִכְלִי אֶחָד. אֲבָל אִם הָיָה אֶחָד מֵהֶן שֻׁתָּף לָזֶה בְּיַיִן וּלְאַחֵר בְּשֶׁמֶן אוֹ שֶׁהָיָה הַכּל יַיִן וְהָיָה בִּשְׁנֵי כֵּלִים הֲרֵי אֵלּוּ צְרִיכִין שִׁתּוּף אַחֵר לְעִנְיַן שַׁבָּת:
כסף משנה
1.
[The following rules apply when] the inhabitants of a lane join in a business partnership with regard to a particular food - i.e., they have bought wine, oil, honey, or the like [for sale]:1A shituf established by the inhabitants of a lane is mentioned because it can be established with other types of food besides bread. In contrast, an eruv for a courtyard may be established only with bread (Chapter 1, Halachah 8). The Rashba (as quoted by the Maggid Mishneh) states that the same principle would apply if the inhabitants of a courtyard established a business partnership for the sale of bread. They need not establish another shituf for the sake [of carrying on] the Sabbath. Instead, they may rely on the partnership they have established for business reasons.
[When does this leniency apply?] When their business partnership involves one type of produce, and [this produce] is stored in a single container. But if their partnership is such that one possesses wine and the other oil,2The Tur (Orach Chayim 366) states that even if the partnership involves several types of produce, as long as it is stored in a single container, the inhabitants may rely on it for the sake of the Sabbath. The Ramah (Orach Chayim 386:3) quotes this ruling. or they both possess wine but hold it in two different containers, they are required to establish another shituf for the sake of the Sabbath.

הלכה ב
אֶחָד מִבְּנֵי הַמָּבוֹי שֶׁבִּקֵּשׁ מֵחֲבֵרוֹ יַיִן אוֹ שֶׁמֶן קֹדֶם הַשַּׁבָּת וְלֹא נָתַן לוֹ בָּטַל הַשִּׁתּוּף. שֶׁהֲרֵי גִּלָּה דַּעְתּוֹ שֶׁאֵינָן כֻּלָּן כְּשֻׁתָּפִין שֶׁאֵין מַקְפִּידִין זֶה עַל זֶה. אֶחָד מִבְּנֵי הַמָּבוֹי שֶׁרָגִיל לְהִשְׁתַּתֵּף עִם בְּנֵי הַמָּבוֹי וְלֹא נִשְׁתַּתֵּף. בְּנֵי מָבוֹי נִכְנָסִין לְבֵיתוֹ וְנוֹטְלִין מִמֶּנּוּ שִׁתּוּף בְּעַל כָּרְחוֹ. וְאֶחָד מִבְּנֵי הַמָּבוֹי שֶׁאֵינוֹ רוֹצֶה לְהִשְׁתַּתֵּף כְּלָל עִם בְּנֵי הַמָּבוֹי כּוֹפִין אוֹתוֹ לְהִשְׁתַּתֵּף עִמָּהֶן:
כסף משנה
2.
If one of the inhabitants of a lane asks another for wine or oil before the Sabbath, and the latter refuses to give it to him, the shituf is nullified.3The Rambam's ruling is based on Eruvin 68a. In his commentary on that passage, Rashi explains that this refers to the food set aside for the shituf. If the person asks for some of this food and it is not given to him, the eruv is nullified.
Although this does not appear to be the Rambam's intent, the Kessef Mishneh explains that his words can be interpreted in this manner. [And in the Shulchan Aruch (Orach Chayim 366:5), Rav Yosef Karo rules according to his explanation in the Kessef Mishneh]. The Ra'avad goes further and explains that this law applies only when one person has granted others a share in his produce for the purpose of establishing a shituf. If, afterwards, he refuses to allow one of the members of the lane to take from the shituf, the shituf is nullified.
[The rationale is that this individual] revealed that his intent was that they are not all to be considered partners who do not object to each other's [use of the combined resources].
When one of the inhabitants of a lane who usually participates in a shituf fails to do so,4With the intent of nullifying the shituf. the inhabitants of the lane may enter his home and take [his share for] the shituf against his will. If one of the inhabitants of a lane refuses5I.e., in contrast to the previous law, this person was not a regular participant in the shituf. to join with the others in the shituf, he may be compelled to do so.6I.e., the communal court may compel him to join the shituf. Nevertheless, in contrast to the previous law, the matter may not be dealt with by the inhabitants of the lane themselves (Maggid Mishneh). This ruling is quoted by the Shulchan Aruch (Orach Chayim 367:1).
The Noda BiY'hudah (Vol. II, Choshen Mishpat, Responsum 39) points to Hilchot Sh'chenim 5:12 (quoted in the Shulchan Aruch, Choshen Mishpat 162:1), which appears to contradict this interpretation, for it states that the members of the lane may compel each other to build a pole or a beam for a courtyard. The Noda BiY'hudah explains, however, that there is a difference between the structure of a courtyard (i.e., the pole or the beam) and participation in an eruv.

הלכה ג
אֶחָד מִבְּנֵי הַמָּבוֹי שֶׁהָיָה לוֹ אוֹצָר שֶׁל יַיִן אוֹ שֶׁמֶן וְכַיּוֹצֵא בָּהֶן הֲרֵי זֶה מְזַכֶּה מִמֶּנּוּ מְעַט לְכָל בְּנֵי הַמָּבוֹי לְהִשְׁתַּתֵּף בּוֹ וּמְעָרֵב בּוֹ עֲלֵיהֶם. וְאַף עַל פִּי שֶׁלֹּא הִפְרִישׁוֹ וְלֹא יִחֲדוֹ אֶלָּא הֲרֵי הוּא מְעֹרָב בָּאוֹצָר הֲרֵי זֶה שִׁתּוּף:
כסף משנה
3.
When one of the inhabitants of a lane owns a storeroom of wine, oil, or the like, he may grant a small share to all the inhabitants of the lane and establish a shituf on their behalf. The shituf is acceptable even though he did not separate or designate [the wine he granted them, but rather left it] mixed together [with the remainder] in the storeroom.

הלכה ד
חָצֵר שֶׁיֵּשׁ לָהּ שְׁנֵי פְּתָחִים לִשְׁנֵי מְבוֹאוֹת אִם נִשְׁתַּתְּפָה עִם אֶחָד מֵהֶן בִּלְבַד נֶאֶסְרָה בַּמָּבוֹי הַשֵּׁנִי וְאֵינָהּ מוֹצִיאָה וּמַכְנִיסָה בּוֹ. לְפִיכָךְ אִם זִכָּה אֶחָד בְּשִׁתּוּף לְכָל בְּנֵי הַמָּבוֹי וְשִׁתֵּף עֲלֵיהֶן צָרִיךְ לְהוֹדִיעַ לְאַנְשֵׁי הֶחָצֵר זוֹ. שֶׁאֵינָן מִשְׁתַּתְּפִין אֶלָּא מִדַּעְתָּן שֶׁאֵינָהּ זְכוּת לָהֶן שֶׁמָּא בַּמָּבוֹי הַשֵּׁנִי רוֹצִים לְהִשְׁתַּתֵּף וְלֹא בָּזֶה:
כסף משנה
4.
[When the inhabitants of] a courtyard that has two entrances, each leading to a different lane, establish a shituf with one of [the lanes] and not the other,7According to most authorities, the inhabitants of such a courtyard have the right to establish a shituf with the inhabitants of both lanes, if they desire. If they chose this option, they may bring articles to and from both lanes. The Maggid Mishneh maintains that the Rambam accepts this view, as well.
There are opinions (see Rabbenu Yehonatan) that maintain that Rabbenu Yitzchak Alfasi differs with this view, and maintains that in such a situation, the inhabitants of the courtyard may join in a shituf with the inhabitants of only one lane. Some maintain that the Rambam also accepts this view. This is surely the opinion of the Ra'avad, who objects to the Rambam's ruling here.
This interpretation cannot be justified in light of the Rambam's ruling in Halachah 7. Accordingly, Merkevet HaMishneh offers a different interpretation of Rabbenu Yitzchak Alfasi's view, as is explained in the following note.
[they] are forbidden to bring articles to and from the second lane.
Therefore, if a person [sets aside food for a shituf], grants a portion to all the inhabitants of the lane, and establishes a shituf on their behalf, he must notify the inhabitants of that courtyard. For they must make a conscious decision to join the shituf, since this is not [necessarily] to their benefit,8In Chapter 1, Halachah 20, the Rambam states: "A person need not inform the inhabitants of a lane or a courtyard that he has granted them [a portion of food] and established an eruv for them, for these deeds are to their benefit, and a person may grant a colleague benefit without the latter's knowledge."
The rationale behind that ruling is that it is surely to the benefit of the inhabitants of a courtyard to be able to bring articles to and from areas outside their courtyard. In this instance, however, the establishment of a shituf is not necessarily to the benefit of the inhabitants of that courtyard, and they must therefore be notified beforehand.
The Maggid Mishneh explains that the shituf is not necessarily to their benefit, because they have another alternative to transfer articles to and from the courtyard from outside. Hence, it is possible that the inhabitants of the courtyard do not desire to join in the shituf with this lane, lest doing so increase the amount of human traffic in their courtyard.
According to Rabbenu Yitzchak Alfasi's view, the question facing the inhabitants of this courtyard is: If they do not join in a shituf with either of the lanes, they are allowed to transfer articles left in the courtyard at the commencement of the Sabbath to and from both the lanes. Should they join in a shituf with only one of the lanes, although their opportunities are greatly increased with regard to transferring articles to and from the lane with which they established the shituf, they lose the opportunity to transfer articles to and from the other lane. Perhaps they would desire to maintain the situation as it was originally rather than forfeit this opportunity.
because it is possible that they desire to join in a shituf with [the inhabitants of] the other lane, and not with this one.

הלכה ה
אִשְׁתּוֹ שֶׁל אָדָם מְעָרֶבֶת לוֹ שֶׁלֹּא מִדַּעְתּוֹ וְהוּא שֶׁלֹּא יֶאֱסרוֹ עַל שְׁכֵנָיו. אֲבָל אִם אוֹסֵר אֵינָהּ מְעָרֶבֶת עָלָיו וְלֹא מִשְׁתַּתֶּפֶת עָלָיו אֶלָּא מִדַּעְתּוֹ. כֵּיצַד אוֹסֵר. כְּגוֹן שֶׁאָמַר אֵינִי מְעָרֵב עִמָּכֶם אוֹ אֵינִי מִשְׁתַּתֵּף עִמָּכֶם:
כסף משנה
5.
A person's wife may participate in an eruv on his behalf without his knowledge, provided he does not [intend to cause] his neighbors to be forbidden [to carry].9In this ruling, the Rambam's interpretation of Eruvin 80a (the source for this halachah) parallels that of Rabbenu Chanan'el. Rashi, the Ra'avad, and others offer a directly opposite interpretation of that passage. The Shulchan Aruch (Orach Chayim 367:1) follows the latter view.
The Ra'avad's objection to the Rambam's ruling revolves around the interpretation of the passage cited above, which begins:

A [gentile] officer lived in Rabbi Zeira's neighborhood. [The Jews] offered to rent his domain on the Sabbath, but he refused.
They came to Rabbi Zeira and asked whether they could rent it from his wife. He told them, "...A person's wife may establish an eruv on his behalf without his knowledge."

According to the Rambam, the law Rabbi Zeira cites as support is not entirely analogous to the situation regarding which he was asked. A Jew's wife may establish an eruv without his knowledge, but not against his will. A gentile's wife, by contrast, may rent out his domain even when he has already refused (Sefer HaKovetz).
If he does [intend to cause] them to be forbidden [to carry], however, she may not join an eruv on his behalf, nor may she join a shituf on his behalf unless he consents.
What is meant by "[intend to cause] them to be forbidden [to carry]"? That he says, "I will not join in an eruv or a shituf with them."

הלכה ו
נִשְׁתַּתְּפוּ אַנְשֵׁי חָצֵר זוֹ עִם אֶחָד מִשְׁנִי הַמְּבוֹאוֹת אִם בְּמִין אֶחָד נִשְׁתַּתְּפוּ אֲפִלּוּ כָּלָה אוֹתוֹ הַמִּין הֲרֵי זֶה עוֹשֶׂה שִׁתּוּף אַחֵר וּמְזַכֶּה לָהֶן וְאֵינוֹ צָרִיךְ לְהוֹדִיעָם פַּעַם שְׁנִיָּה. וְאִם בִּשְׁנֵי מִינִין נִשְׁתַּתְּפוּ וְנִתְמַעֵט הָאֹכֶל מוֹסִיף וּמְזַכֶּה וְאֵינוֹ צָרִיךְ לְהוֹדִיעָן. וְאִם כָּלוּ מְזַכֶּה לָהֶם וְצָרִיךְ לְהוֹדִיעָם. נִתְוַסְּפוּ שְׁכֵנִים בֶּחָצֵר זוֹ מְזַכֶּה לָהֶם וְצָרִיךְ לְהוֹדִיעָם:
כסף משנה
6.
[The following rules apply when a courtyard opens up to two lanes and] the inhabitants of the courtyard have established a shituf with [the inhabitants of] one of the lanes: If they had originally established the shituf with one type of produce, even if the produce in the shituf was consumed entirely, one may establish a second shituf and grant them a portion; there is no need to inform them a second time.10Since they agreed to join in the shituf previously, we assume that they desire to continue the arrangement (Levush, Orach Chayim 368:1).
If they have established the shituf with two types11Rashi (Eruvin 80b) explains that this refers to establishing the second shituf with a different type of produce, rather than establishing the first eruv with two types of produce. His approach is cited by the Shulchan Aruch (Orach Chayim 368:1). of produce,12Note Chapter 1, Halachah 11, where the Rambam states that a shituf can be established using two types of produce. The Ra'avad objects both there and here. and the amount of food was reduced [from the minimum required],13See Chapter 1, Halachah 9. one may add to it and grant the others a share; there is no need to inform them. If [the produce] was consumed entirely, one may [establish a second shituf and] grant them a portion; it is, however, necessary to inform them.14Merkevet HaMishneh explains that, even according to the Rambam, using two types of produce for a shituf is undesirable. Therefore, if the shituf must be established anew, it is necessary to check whether the inhabitants of the lane consent.
If the number of inhabitants within the courtyard is increased, one may grant [the newcomers] a portion in the shituf, but one must notify them.15For perhaps they would desire to establish the shituf with the inhabitants of the other lane.

הלכה ז
נִשְׁתַּתְּפָה חָצֵר זוֹ עִם בְּנֵי הַמָּבוֹי זֶה מִפֶּתַח זֶה וְעִם בְּנֵי הַמָּבוֹי הַשֵּׁנִי מִן הַפֶּתַח הָאַחֵר מֻתֶּרֶת עִם שְׁנֵיהֶן וְהֵן מֻתָּרִין עִמָּהּ וּשְׁנֵי הַמְּבוֹאוֹת אֲסוּרִין זֶה עִם זֶה. לֹא עֵרְבָה עִם אֶחָד מֵהֶם אוֹסֶרֶת עַל שְׁנֵיהֶן:
כסף משנה
7.
If the inhabitants of this courtyard have established a shituf with the inhabitants of this lane from one entrance, and have established another shituf with the inhabitants of the other lane from the other entrance, they are permitted [to carry to and from] both [of these lanes]16See the notes on Halachah 4., and [the inhabitants of] both [lanes] are permitted [to carry within the courtyard]. [The inhabitants of] both lanes are, however, forbidden [to carry] from one [lane] to the other.17Unless they join together in a shituf.
If [the inhabitants of the courtyard] have not established a shituf with either of them, they cause [the inhabitants of] both to be forbidden [to carry].18Since there is a courtyard in their lane that has not joined in the shituf, all the inhabitants of the lane are forbidden to carry.

הלכה ח
הָיְתָה חָצֵר זוֹ רְגִילָה בְּפֶתַח אֶחָד וְהַפֶּתַח הַשֵּׁנִי אֵינָהּ רְגִילָה. זֶה שֶׁרְגִילָה לְהִכָּנֵס וְלָצֵאת בּוֹ אוֹסֵר וְשֶׁאֵינָהּ רְגִילָה בּוֹ אֵינוֹ אוֹסֵר. עֵרְבָה עִם מָבוֹי שֶׁאֵינָהּ רְגִילָה בּוֹ הֻתַּר הַמָּבוֹי הָאַחֵר לְעַצְמוֹ וְאֵינוֹ צָרִיךְ לְעָרֵב עִמָּהּ:
כסף משנה
8.
[The following rules apply when the inhabitants of] this courtyard usually [pass] through one entrance [into one lane], but do not usually [pass] through a second entrance [into another lane]: They cause carrying to be forbidden [in the lane to which] the entrance through which they usually [pass opens].19Unless they join in a shituf. They do not cause carrying to be forbidden [in the lane to which] the entrance through which they do not usually [pass opens].20Even when they do not join in a shituf.
If [the inhabitants of this courtyard] have established a shituf with [only] the lane through which they do not usually [pass], [the inhabitants of] the other lane are allowed [to carry];21Provided they establish an eruv for themselves. they do not have to establish a shituf with [the inhabitants of this courtyard].

הלכה ט
עֵרְבוּ בְּנֵי הַמָּבוֹי שֶׁהִיא רְגִילָה בּוֹ לְעַצְמָן וְהִיא לֹא עֵרְבָה עִמּוֹ וְלֹא עִם בְּנֵי הַמָּבוֹי הָאַחֵר שֶׁאֵינָהּ רְגִילָה בּוֹ וְגַם לֹא עֵרְבוּ בְּנֵי הַמָּבוֹי שֶׁאֵינָהּ רְגִילָה בּוֹ. דּוֹחִין אוֹתָהּ אֵצֶל זֶה הַמָּבוֹי שֶׁאֵינָהּ רְגִילָה מִפְּנֵי שֶׁלֹּא עֵרֵב. הוֹאִיל וְהִיא לֹא עֵרְבָה וְהוּא לֹא עֵרֵב דּוֹחִין אוֹתָהּ אֶצְלוֹ כְּדֵי שֶׁלֹּא תֶּאֱסֹר עַל מָבוֹי זֶה שֶׁעֵרֵב לְעַצְמוֹ:
כסף משנה
9.
[A leniency is granted in the following situation.] The inhabitants of the lane [through] which [the inhabitants of] this courtyard usually pass established a shituf by themselves. [The inhabitants of the courtyard] did not join in this shituf, nor have they joined in a shituf with the inhabitants of the lane [through] which they do not usually pass. The inhabitants of the latter lane [also] did not establish a shituf for themselves.
Since [the inhabitants of the courtyard] have not joined in a shituf at all, they are considered part of the lane [through] which they do not usually pass. Since both these groups of individuals have not established a shituf, they are classed together, so that they will not cause [the inhabitants of] the lane who established the shituf to be forbidden [to carry].22Based on the principles stated in the previous halachah, it would seem that the fact that the inhabitants of this courtyard have not joined in the shituf of the lane through which they usually pass would cause carrying to be forbidden in this lane. Nevertheless, since the inhabitants of this courtyard have another alternative, they are considered part of the courtyard through which they do not usually pass. The rationale is that through this decision, one group of people (the inhabitants of the lane who established a shituf) benefits (for their shituf is considered acceptable), and another group (the inhabitants of the courtyard in question) does not lose (for they are forbidden to carry regardless) [Eruvin 49a].

הלכה י
חָצֵר שֶׁיֵּשׁ לָהּ פֶּתַח לְמָבוֹי וּפֶתַח אַחֵר לְבִקְעָה אוֹ לְקַרְפָּף יֶתֶר מִבֵּית סָאתַיִם הוֹאִיל וְאָסוּר לְטַלְטֵל מֵחָצֵר לְאוֹתוֹ הַקַּרְפָּף אֵינוֹ סוֹמֵךְ אֶלָּא עַל פֶּתַח שֶׁל מָבוֹי לְפִיכָךְ אוֹסֵר עַל בְּנֵי הַמָּבוֹי עַד שֶׁיִּשְׁתַּתֵּף עִמָּהֶן. אֲבָל אִם הָיָה הַקַּרְפָּף בֵּית סָאתַיִם אוֹ פָּחוֹת אֵינוֹ אוֹסֵר עַל בְּנֵי הַמָּבוֹי שֶׁעַל הַפֶּתַח הַמְיֻחָד לוֹ סוֹמֵךְ הוֹאִיל וּמֻתָּר לְטַלְטֵל בְּכָל הַקַּרְפָּף:
כסף משנה
10.
[The following rules apply when] a courtyard has an entrance to a lane and another entrance to a valley or to an area enclosed for purposes other than habitation, which is larger than the area [needed] to sow two se'ah:23As the Rambam explains in Hilchot Shabbat 16:3, this is an area of 5000 square cubits. The Sages forbade carrying in such an area, even when it is surrounded by a proper partition (loc. cit.:1-2). Since it is forbidden to transfer articles from the courtyard to that enclosed area, [the inhabitants of the courtyard] rely only on the entrance to the lane. Therefore, they cause the inhabitants of the lane to be forbidden [to carry] unless they join together with them in a shituf.
If, however, the enclosed area is the size of the area [needed] to sow two se'ah or less, its presence does not cause the inhabitants of the lane to be forbidden [to carry]. Since carrying is permitted within the entire enclosed area, [the inhabitants of the courtyard] rely on the entrance that is exclusively theirs.24I.e., we assume that the entrance that is more important to them is the entrance to the enclosed area and not the entrance to the lane. Hence, the fact that they have an entrance to the lane is of no significance.

הלכה יא
אֶחָד מִבְּנֵי מָבוֹי שֶׁהָלַךְ לִשְׁבֹּת בְּמָבוֹי אַחֵר אֵינוֹ אוֹסֵר עֲלֵיהֶן. וְכֵן אֶחָד מִבְּנֵי מָבוֹי שֶׁבָּנָה מַצֵּבָה רְחָבָה אַרְבָּעָה טְפָחִים עַל פִּתְחוֹ אֵינוֹ אוֹסֵר עֲלֵיהֶן שֶׁהֲרֵי הִפְרִישׁ עַצְמוֹ מֵהֶן וְחָלַק רְשׁוּתוֹ:
כסף משנה
11.
When one of the inhabitants of a lane goes away and spends the Sabbath in another place, [the fact that he owns a domain in the lane] does not cause carrying to be forbidden.25See Chapter 4, Halachah 13.
Similarly, if one of the inhabitants of a lane builds a pillar that is four handbreadths wide [or more] before his entrance, [the fact that he owns a domain in the lane] does not cause carrying to be forbidden. For he has separated himself from [the other inhabitants], and has made his domain a distinct entity.26See also Halachah 24 and Chapter 4, Halachah 16.

הלכה יב
אַנְשֵׁי מָבוֹי שֶׁנִּשְׁתַּתְּפוּ מִקְצָתָן וְשָׁכְחוּ מִקְצָתָן וְלֹא נִשְׁתַּתְּפוּ מְבַטְּלִין רְשׁוּתָן לְאֵלּוּ שֶׁנִּשְׁתַּתְּפוּ. וְדִינָם לְעִנְיַן בִּטּוּל רְשׁוּת כְּדִין אַנְשֵׁי חָצֵר שֶׁשָּׁכַח אֶחָד מֵהֶן אוֹ שְׁנַיִם וְלֹא עֵרְבוּ. וּכְבָר אָמַרְנוּ שֶׁכָּל אָדָם עִם אַנְשֵׁי בֵּיתוֹ הַסְּמוּכִים עַל שֻׁלְחָנוֹ כְּאִישׁ אֶחָד הֵן חֲשׁוּבִין בֵּין לְעֵרוּבֵי חֲצֵרוֹת בֵּין לְשִׁתּוּפֵי מְבוֹאוֹת:
כסף משנה
12.
[The following rules apply when] the inhabitants of a lane have joined together in a shituf, but several of the inhabitants forgot and did not join: [Those who forgot] should subordinate the ownership of their domain to those who joined in the shituf. The laws governing the subordination of the ownership of their domain are the same as the laws governing the subordination of the ownership of a domain when one or more of the inhabitants of a courtyard forgot to join in an eruv.27See Chapter 2, Halachot 1-5.
We have already explained28Chapter 4, Halachah 1. that a person and [all] the members of his household who are dependent on him for meals are considered to be a single entity with regard to the establishment of an eruv for a courtyard and a shituf for a lane.

הלכה יג
מָבוֹי שֶׁעֵרְבוּ כָּל חֲצֵרוֹת שֶׁבּוֹ כָּל חָצֵר וְחָצֵר בִּפְנֵי עַצְמָהּ וְאַחַר כָּךְ נִשְׁתַּתְּפוּ כֻּלָּן בַּמָּבוֹי. שָׁכַח אֶחָד מִבְּנֵי הֶחָצֵר וְלֹא עֵרֵב עִם בְּנֵי חֲצֵרוֹ לֹא הִפְסִיד כְּלוּם. שֶׁהֲרֵי כֻּלָּם נִשְׁתַּתְּפוּ וְעַל הַשִּׁתּוּף סוֹמְכִין וְלֹא הִצְרִיכוּ לְעָרֵב בַּחֲצֵרוֹת עִם הַשִּׁתּוּף אֶלָּא שֶׁלֹּא לְשַׁכֵּחַ לַתִּינוֹקוֹת תּוֹרַת עֵרוּב וַהֲרֵי עֵרְבוּ בַּחֲצֵרוֹת. אֲבָל אִם שָׁכַח אֶחָד מִבְּנֵי הַמָּבוֹי וְלֹא נִשְׁתַּתֵּף אֲסוּרִים בַּמָּבוֹי וּמֻתָּרִין כָּל בְּנֵי חָצֵר לְטַלְטֵל בַּחֲצֵרָן שֶׁהַמָּבוֹי לַחֲצֵירוֹת כְּחָצֵר לַבָּתִּים:
כסף משנה
13.
[The following rules apply when the inhabitants of] all the courtyards established eruvin for each of the courtyards, and afterwards they all joined in a shituf for the lane: When one of the inhabitants of a lane forgot to join in the eruv with the other inhabitants of his courtyard, he does not lose any [privileges]. For all of them have joined together in a shituf, and it is on the shituf that they rely.
The only reason it was required to establish an eruv within the courtyards, together with the shituf, is so that the children will not forget the law of the eruv.29I.e., an eruv established within a courtyard will be seen by the children, and they will know that it is only because of this eruv that the restrictions against carrying are relaxed. If, however, there is only a shituf in the lane, it is unlikely to be noticed by the children, and they will not know about the restrictions established by our Sages (Eruvin 73b). (See, however, the notes on the following halachah.) [And in this instance, that requirement has been met,] for eruvin were established in the courtyards.
If, however, one of the inhabitants of the lane forgot to join in the shituf, carrying is forbidden in the lane.30For the shituf requires the participation of all the inhabitants of the lane. The inhabitants of the courtyards, however, may carry in their [respective] courtyards. [When a shituf is not established,] the relationship between courtyards and a lane is parallel to that between homes and a courtyard.31See Halachah 15.

הלכה יד
נִשְׁתַּתְּפוּ בַּמָּבוֹי וְשָׁכְחוּ כֻּלָּן לְעָרֵב בָּחֲצֵרוֹת. אִם אֵין מַקְפִּידִין עַל פְּרוּסָתָן סוֹמְכִין עַל הַשִּׁתּוּף בַּשַּׁבָּת הָרִאשׁוֹנָה בִּלְבַד. וְאֵין מַתִּירִין לָהֶן דָּבָר זֶה אֶלָּא מִדֹּחַק:
כסף משנה
14.
[The following rules apply when the inhabitants of all the courtyards] have joined in a shituf, but all have forgotten to establish eruvin for their respective courtyards: If they do not stint on sharing their bread,32I.e., if one person will give a colleague bread - other than the bread of the shituf - when asked (Ra'avad, Maggid Mishneh, based on the Jerusalem Talmud, Eruvin 6:8). they may rely on the shituf for one Sabbath alone. This leniency is granted, however, only because of the difficulty [of their immediate circumstance].33Rav Moshe HaCohen notes an apparent contradiction between this halachah and Chapter 1, Halachah 19, which states that if a shituf was established with bread, there is no need for eruvin within the courtyards, because the children will be aware of the collection of loaves of bread. He maintains that this leniency may be accepted at all times. The Shulchan Aruch (Orach Chayim 387:1) accepts this view.
The Ramah mentions an even greater leniency. He maintains that we may rely on the shituf although eruvin were not established, even when the shituf was established with wine or other foods. His rationale is that in Talmudic times, the shituf was established by one member of each courtyard, who acted on behalf of all the inhabitants. At present, however, all the inhabitants of the lane contribute individually to the shituf.
This rationale is not accepted by the later authorities; Shulchan Aruch HaRav 387:1 and the Mishnah Berurah 387:12 suggest following the opinion of the Shulchan Aruch.

הלכה טו
מָבוֹי שֶׁלֹּא נִשְׁתַּתְּפוּ בּוֹ אִם עֵרְבוּ חֲצֵרוֹת עִם הַבָּתִּים אֵין מְטַלְטְלִין בּוֹ אֶלָּא בְּאַרְבַּע אַמּוֹת כְּכַרְמְלִית. מֵאַחַר שֶׁעֵרְבוּ חֲצֵרוֹת עִם הַבָּתִּים נַעֲשָׂה הַמָּבוֹי כְּאִלּוּ אֵינוֹ פָּתוּחַ לוֹ אֶלָּא בָּתִּים בִּלְבַד בְּלֹא חֲצֵרוֹת. וּלְפִיכָךְ אֵין מְטַלְטְלִין בְּכֻלָּן. וְאִם לֹא עֵרְבוּ אַנְשֵׁי הַחֲצֵרוֹת מְטַלְטְלִין בְּכֻלָּן כֵּלִים שֶׁשָּׁבְתוּ בְּתוֹכוֹ כְּחָצֵר שֶׁלֹּא עֵרְבוּ בָּהּ:
כסף משנה
15.
When eruvin have been established between the courtyards and the homes [of a lane], but a shituf has not been established, carrying [an article] more than four cubits [within the lane] is forbidden, as [would be the law] within a carmelit.
[The rationale is that] since eruvin were established between the courtyards and the homes, the lane is considered as though it opened only to homes, and not to courtyards. Therefore, we are not allowed to carry within its area at all.34The Rambam's ruling is based on his conception [Hilchot Shabbat 17:8; Commentary on the Mishnah (Eruvin 6:8)] that a lane must have several courtyards and several houses open to it.
The Ra'avad, Rav Moshe HaCohen, and others object to the Rambam's ruling, explaining that it follows the opinion of Rav (Shabbat 131a). Nevertheless, the halachah ultimately follows the view of Shmuel (Eruvin 74a), who maintains that the lane and the courtyards are considered to be a single entity. According to this view, when a shituf has not been established, there is no difference whether or not eruvin have been established within the courtyards. Shulchan Aruch HaRav 388:1 and the Mishnah Berurah 388:4 rule according to this view.
The Mishnah Berurah adds that the stringency suggested by the Rambam applies only when the open side of the lane is adjusted with a pole or a beam. If, however, the open side is adjusted with a frame of an entrance, even the Rambam would agree that one is permitted to carry articles that were left in the lane at the beginning of the Sabbath.

If the inhabitants of the courtyards have not established eruvin, they may carry articles left in the [lane] at the commencement of the Sabbath throughout its entire area, as is the law regarding a courtyard in which an eruv was not established.35See Chapter 3, Halachot 18-19.

הלכה טז
עוֹבֵד כּוֹכָבִים אוֹ צְדוֹקִי הַשָּׁרוּי בְּחָצֵר שֶׁבַּמָּבוֹי דִּינוֹ עִם בְּנֵי הַמָּבוֹי כְּדִינוֹ עִם בְּנֵי הֶחָצֵר שֶׁשּׂוֹכְרִים מִן הָעוֹבֵד כּוֹכָבִים אוֹ מֵאֶחָד מִבְּנֵי בֵּיתוֹ רְשׁוּתוֹ שֶׁבַּמָּבוֹי. אוֹ מְבַטֵּל לָהֶן הַצְּדוֹקִי. וְאִם הָיָה בַּמָּבוֹי עוֹבֵד כּוֹכָבִים וְיִשְׂרָאֵל אֶחָד אֵינוֹ צָרִיךְ שִׁתּוּף. וְדִין יִשְׂרָאֵל אֶחָד וְדִין רַבִּים שֶׁהֵן סוֹמְכִין עַל שֻׁלְחָן אֶחָד דִּין אֶחָד הוּא:
כסף משנה
16.
The laws that the inhabitants of a lane must follow with regard to a gentile36See Chapter 2, Halachah 10. or a Sadducee37See Chapter 2, Halachah 16. who dwells in one of the courtyards of a lane are the same as must be followed by the inhabitants of the courtyard. They must rent the gentile's domain within the courtyard from him or from one of the members of his household, and the Sadducee must subordinate the ownership of his domain.
If [only] one Jew and a gentile were dwelling in the lane, a shituf is not necessary.38See Chapter 2, Halachah 9. The same laws apply when many individuals [are members of one household and] rely on that household for their substance [and these individuals share a lane with a gentile].39See Chapter 4, Halachah 1.

הלכה יז
עוֹבֵד כּוֹכָבִים שֶׁהָיָה דָּר בַּמָּבוֹי אִם יֵשׁ לוֹ בַּחֲצֵרוֹ פֶּתַח אֶחָד לַבִּקְעָה אֵינוֹ אוֹסֵר עַל בְּנֵי הַמָּבוֹי. וַאֲפִלּוּ הָיָה פֶּתַח קָטָן אַרְבָּעָה עַל אַרְבָּעָה. וְאַף עַל פִּי שֶׁמּוֹצִיא גְּמַלִּים וּקְרוֹנוֹת דֶּרֶךְ הַפֶּתַח שֶׁבַּמָּבוֹי אֵינוֹ אוֹסֵר עֲלֵיהֶן שֶׁאֵין דַּעְתּוֹ אֶלָּא עַל פֶּתַח הַמְיֻחָד לוֹ שֶׁהוּא לַבִּקְעָה. וְכֵן אִם הָיָה פָּתוּחַ לְקַרְפָּף שֶׁהוּא יֶתֶר עַל בֵּית סָאתַיִם הֲרֵי זֶה כְּפָתוּחַ לַבִּקְעָה וְאֵינוֹ אוֹסֵר עֲלֵיהֶן. הָיָה בֵּית סָאתַיִם אוֹ פָּחוֹת אֵינוֹ סוֹמֵךְ עֲלֵיהֶן וְאוֹסֵר עֲלֵיהֶן עַד שֶׁיִּשְׂכְּרוּ מִמֶּנּוּ:
כסף משנה
17.
When a gentile living in a lane has an opening40We have translated the Hebrew פתח as "opening," rather than "entrance," in light of the ruling of the Shulchan Aruch (Orach Chayim 389:1) that a window is sufficient. from his courtyard to a valley, his presence does not cause [carrying] to be forbidden within the lane [although his courtyard also opens to the lane].41As reflected by Halachah 10, when a person has one entrance that is semi-private and another that is more public, the entrance that is more private is considered to be the one he will prefer. Since the gentile has an alternative of this nature, his presence does not cause carrying to be forbidden within the lane. Even if this entrance is small - merely four [handbreadths] by four [handbreadths] - and the gentile leads his camels and his wagons out through the other entrance, his presence does not cause [carrying] to be forbidden. For he is concerned only with the entrance that is distinctly his own - i.e., [the one leading to] the valley.
Similarly, if he has an entrance leading to an area that was enclosed for purposes other than habitation, [and that entrance] is larger than the area needed to sow two se'ah [of grain], it is regarded like an entrance to a valley, and his presence does not cause [carrying] to be forbidden. If, however, the enclosed area was the size needed to sow two se'ah of grain or less, [the gentile] is not concerned with [this area],42Because of its small size. and his presence causes [carrying] to be forbidden,43Significantly, these laws are directly opposite to those applying to a Jew, as mentioned in Halachah 10. unless [his domain] is rented from him.

הלכה יח
מָבוֹי שֶׁצִּדּוֹ אֶחָד עוֹבֵד כּוֹכָבִים וְצִדּוֹ אֶחָד יִשְׂרְאֵלִים וְהָיוּ חַלּוֹנוֹת פְּתוּחוֹת מֵחָצֵר לֶחָצֵר שֶׁל יִשְׂרָאֵל וְעֵרְבוּ כֻּלָּן דֶּרֶךְ חַלּוֹנוֹת. אַף עַל פִּי שֶׁנַּעֲשׂוּ כְּאַנְשֵׁי בַּיִת אֶחָד וּמֻתָּרִין לְהוֹצִיא וּלְהַכְנִיס דֶּרֶךְ חַלּוֹנוֹת הֲרֵי אֵלּוּ אֲסוּרִין לְהִשְׁתַּמֵּשׁ בַּמָּבוֹי דֶּרֶךְ פְּתָחִים עַד שֶׁיִּשְׂכְּרוּ מִן הָעוֹבֵד כּוֹכָבִים. שֶׁאֵין נַעֲשִׂים כְּיָחִיד בִּמְקוֹם עוֹבֵד כּוֹכָבִים:
כסף משנה
18.
[The following rule applies when] there is a lane that has gentiles living [in the courtyards] on one side and Jews living [in the courtyards] on the other side, and there are windows that open from each of the courtyards in which the Jews [live] to the other: Although they established eruvin via the windows, and thus are joined together as the members of a single household - and are, therefore, permitted to transfer [articles] to and from [one courtyard to another] via the windows - they are, nevertheless, forbidden to use the lane via its entrances44I.e., one might think that since they are joined together as a single entity, the leniency mentioned in the final clause of Halachah 16 would apply. This, however, is not the case, as the Rambam proceeds to state. unless they rent the domains from the gentiles. For the principle that [because of an eruv] the many become considered a single entity does not apply when there are gentiles involved.45See Chapter 2, Halachah 15.

הלכה יט
כֵּיצַד מִשְׁתַּתְּפִין בַּמְּדִינָה. כָּל חָצֵר וְחָצֵר מְעָרֶבֶת לְעַצְמָהּ שֶׁלֹּא לְשַׁכֵּחַ הַתִּינוֹקוֹת. וְאַחַר כָּךְ מִשְׁתַּתְּפִין כָּל אַנְשֵׁי הַמְּדִינָה כְּדֶרֶךְ שֶׁמִּשְׁתַּתְּפִין בַּמָּבוֹי. וְאִם הָיְתָה הַמְּדִינָה קִנְיַן יָחִיד אֲפִלּוּ נַעֲשֵׂית שֶׁל רַבִּים מִשְׁתַּתְּפִין כֻּלָּן שִׁתּוּף אֶחָד וִיטַלְטְלוּ בְּכָל הַמְּדִינָה. וְכֵן אִם הָיְתָה שֶׁל רַבִּים וְיֵשׁ לָהּ פֶּתַח אֶחָד מִשְׁתַּתְּפִין כֻּלָּן שִׁתּוּף אֶחָד:
כסף משנה
19.
How is a shituf established in a city?46This refers to a city surrounded by a wall that has gates, for in this way it is a private domain according to the Torah (Maggid Mishneh). Other authorities - and these are the views accepted by many today - accept the possibility of a city's being encompassed by an eruv consisting of wires or string that forms an imaginary wall. The acceptability of such an enclosure is discussed in Hilchot Shabbat 16:16 and notes. Every courtyard should establish an eruv for itself, so that the children will not forget [the laws of eruvin]. Afterwards, all the inhabitants of the city join together in a shituf in the same way as a shituf is established in a lane.
If the city had once been the property of a single individual, even if later it became the property of many individuals, it is possible for all [the inhabitants] to join in a single shituf and [be permitted] to carry throughout the entire city.47I.e., in contrast to the situation mentioned in the following halachah, there is no need to set a certain area outside the eruv. Similarly, although a city is owned by many, if it has only one entrance, all [the inhabitants] may join in a single shituf.48Since the city has only one entrance, it does not resemble a public domain, and the chance that people will develop a misconception is far less. Hence, no additional measure is necessary (Mishnah Berurah 292:5).

הלכה כ
אֲבָל אִם הָיְתָה שֶׁל רַבִּים וְיֵשׁ לָהּ שְׁנֵי פְּתָחִים שֶׁהָעָם נִכְנָסִין בָּזֶה וְיוֹצְאִין בָּזֶה אֲפִלּוּ נַעֲשֵׂית שֶׁל יָחִיד אֵין מְעָרְבִין אֶת כֻּלָּהּ אֶלָּא מַנִּיחִין מִמֶּנָּה מָקוֹם אֶחָד אֲפִלּוּ בַּיִת אֶחָד בְּחָצֵר אַחַת וּמִשְׁתַּתְּפִין הַשְּׁאָר. וְיִהְיוּ אֵלּוּ הַמִּשְׁתַּתְּפִין כֻּלָּן מֻתָּרִין בְּכָל הַמְּדִינָה חוּץ מֵאוֹתוֹ מָקוֹם שֶׁשִּׁיְּרוּ. וְיִהְיוּ אוֹתָן הַנִּשְׁאָרִים מֻתָּרִין בִּמְקוֹמָן בַּשִּׁתּוּף שֶׁעוֹשִׂין לְעַצְמָן אִם הָיוּ הַנִּשְׁאָרִים רַבִּים. וַאֲסוּרִין לְטַלְטֵל בִּשְׁאָר כָּל הַמְּדִינָה:
כסף משנה
20.
If, by contrast, [a city] was originally built as the property of many individuals,49This represents the Rambam's interpretation of Eruvin 59a,b. The Rashba and the Ritba offer similar, but slightly different interpretations of the passage. Significantly, Rashi interprets the Hebrew עיר של רבים as referring to a city populated by more than 600,000. His view is cited in Shulchan Aruch HaRav 392:1 and the Mishnah Berurah 392:7 as an explanation for the reason that this law is not practiced at present. and it has two openings used for entrance and egress, the entire [city] may not be included in the eruv. [This applies even if the city later] becomes the private property of one individual. Instead, one area - even one house in one courtyard - is set aside,50For the reasons explained in the following halachah. and a shituf is established in the remainder [of the city].
All the individuals who participate in the shituf are permitted [to carry] throughout the entire city with the exception of the place that was set aside. If there are many people [living in] the place [that was set aside], they are permitted to carry in that place if they make a shituf for themselves. They are, however, forbidden to carry throughout the remainder of the city.

הלכה כא
וְדָבָר זֶה מִשּׁוּם הֶכֵּר הוּא כְּדֵי שֶׁיֵּדְעוּ שֶׁהָעֵרוּב הִתִּיר לָהֶן לְטַלְטֵל בִּמְדִינָה זוֹ שֶׁרַבִּים בּוֹקְעִין בָּהּ. שֶׁהֲרֵי הַמָּקוֹם שֶׁנִּשְׁאַר וְלֹא נִשְׁתַּתֵּף עִמָּהֶן אֵין מְטַלְטְלִין בּוֹ אֶלָּא אֵלּוּ לְעַצְמָן וְאֵלּוּ לְעַצְמָן:
כסף משנה
21.
This was instituted to make a distinction, so that [the inhabitants know that the eruv made carrying possible in this large city through which many people pass.51Since the city resembles a public domain, allowing people to carry might create a misconception. Unless a portion of the city were set aside, it is possible that some might entirely lose awareness of the prohibition against carrying. [For they will see] the place that was set aside, which did not join in the shituf, in which carrying is forbidden. [Each group of individuals, the inhabitants of the city and the inhabitants of the area that was set aside] will have their separate [area].

הלכה כב
מְדִינָה שֶׁל רַבִּים שֶׁיֵּשׁ לָהּ פֶּתַח אֶחָד וְסֻלָּם בְּמָקוֹם אֶחָד מְעָרְבִין אֶת כֻּלָּהּ וְאֵינָהּ צְרִיכָה שִׁיּוּר שֶׁאֵין הַסֻּלָּם שֶׁבַּחוֹמָה חָשׁוּב כְּפֶתַח. הַבָּתִּים שֶׁמַּנִּיחִין אוֹתוֹ שִׁיּוּר אַף עַל פִּי שֶׁאֵינָן פְּתוּחִין לָעִיר אֶלָּא אֲחוֹרֵיהֶן לָעִיר וּפְנֵיהֶם לַחוּץ עוֹשִׂין אוֹתוֹ שִׁיּוּר וּמְעָרְבִין אֶת הַשְּׁאָר:
כסף משנה
22.
When a city belonging to many individuals has one entrance and has a ladder52Or even several ladders (Shulchan Aruch, Orach Chayim 392:2). [that could be used to enter or depart] at another place [in its wall], it [is possible to include] the entire [city] in the eruv; no portion need be set aside. For a ladder in the wall is not considered to be an entrance.53Although at times a ladder is considered to be an entrance (e.g., Chapter 3, Halachah 2), this instance is judged by different criteria.
The houses that are set aside [and are not included in the shituf] need not face the city. Even if they face the outside area, and their back is towards the city, they may be [designated as the houses that are] set aside, and then an eruv may be established throughout the remainder [of the city].54These individuals are less likely to be upset about being excluded from the eruv of the city. (See Eruvin 60a.)

הלכה כג
הַמְזַכֶּה בְּשִׁתּוּף לִבְנֵי הַמְּדִינָה. אִם עֵרְבוּ כֻּלָּן עֵרוּב אֶחָד אֵינוֹ צָרִיךְ לְהוֹדִיעָן שֶׁזְּכוּת הוּא לָהֶן. וְדִין מִי שֶׁשָּׁכַח וְלֹא נִשְׁתַּתֵּף עִם בְּנֵי הַמְּדִינָה אוֹ מִי שֶׁהָלַךְ לִשְׁבֹּת בְּעִיר אַחֶרֶת אוֹ עוֹבֵד כּוֹכָבִים שֶׁהָיָה עִמָּהֶן בַּמְּדִינָה דִּין הַכּל כְּדִינָם בְּחָצֵר וּמָבוֹי:
כסף משנה
23.
When a person grants a portion in the shituf to all the inhabitants of a city,55See Chapter 1, Halachah 20. if all the inhabitants join in the same shituf56The Maggid Mishneh (cited also by the Mishnah Berurah 392:34) notes that the Rambam's wording implies that if only a portion of the inhabitants of a city join in the shituf, we do not automatically assume that a person would prefer to be part of them. Perhaps he would prefer to be associated with those who were not included. he is not required to inform them, for [being included] is to their advantage.
The laws that apply to a person who forgot and did not join in a shituf with the inhabitants of a city,57See Chapter 2, Halachah 1. to one who spent the Sabbath in another city,58See Chapter 4, Halachah 13. or to a situation in which gentiles are present59See Chapter 2, Halachah 9; Chapter 4, Halachah 13; and Halachah 16 of the present chapter. in the city are the same as those that apply in a courtyard and in a lane.60Today, when eruvin are made in cities where Jews and gentiles live together, the gentiles' domains are usually rented through an arrangement negotiated with the municipal authorities. Since these authorities have a certain dimension of control over all land under their jurisdiction, and can enter all homes with a court order, they are entitled to rent the domain for all the gentiles living in this area.

הלכה כד
מְדִינָה שֶׁנִּשְׁתַּתְּפוּ כָּל יוֹשְׁבֶיהָ חוּץ מִמָּבוֹי אֶחָד הֲרֵי זֶה אוֹסֵר עַל כֻּלָּן. וְאִם בָּנוּ מַצֵּבָה עַל פֶּתַח הַמָּבוֹי אֵינוֹ אוֹסֵר לְפִיכָךְ אֵין מְעָרְבִין מְדִינָה לַחֲצָאִין אֶלָּא אוֹ כֻּלָּהּ אוֹ מָבוֹי מָבוֹי. וּבוֹנֶה כָּל מָבוֹי וּמָבוֹי מַצֵּבָה עַל פִּתְחוֹ אִם רָצָה לַחֲלֹק רְשׁוּתוֹ מֵהֶן כְּדֵי שֶׁלֹּא יֶאֱסֹר עַל שְׁאָר הַמְּבוֹאוֹת:
כסף משנה
24.
When all the inhabitants of a city with the exception of the inhabitants of a single lane join together in a shituf, [the presence of these individuals] causes [carrying] to be forbidden for all. [The inhabitants] should61Merkevet HaMishneh explains that the Rambam's wording implies that the inhabitants must either join in the shituf or erect a pillar. build a pillar62See Chapter 4, Halachah 16; and Halachah 11 of the present chapter. at the entrance to the lane, so that [carrying] is not forbidden.
For this reason, a shituf is not established in half a city.63The Maggid Mishneh (in his gloss on Halachah 19) and the Shulchan Aruch (Orach Chayim 392:5) interpret this to be referring to a city that is surrounded by a wall with gates.
The Rambam's intent is interpreted to mean that if the pillar is erected in the middle of the public domain, it is not sufficient to divide one part of the city from the other.
If the city is not surrounded by a wall, it is not a private domain according to Torah law. It is possible to enclose a portion by using a Halachic conception of an enclosure, a tzurat hapetach, "a frame of an entrance," but the entire city may not be enclosed in this manner.
Either the entire city joins in the shituf or [separate shitufim are made], each lane for itself. Each lane should build a pillar at its entrance to keep its domain distinct from the others, so that it will not cause [the inhabitants of] the other lanes to be forbidden [to carry].

זמנים הלכות עירובין פרק ה
Zemanim Eruvin Chapter 5