Talmud - Eruvin 89a עירובין פ״ט א׳

They taught this halakha only with regard to a case where the residents of the two upper stories did not establish an eiruv together, but if they established a joint eiruv, they are all permitted to pour water into the courtyard.

The Gemara asks: And where they did not establish an eiruv, what is the reason that the residents who did not dig a pit may not pour water into the courtyard? Rav Ashi said: It is a decree, lest people come to take out vessels filled with water from their houses into the courtyard, to pour into the pit. In the absence of an eiruv, this practice is prohibited.

MISHNA: All the roofs of the city are considered one domain. It is permitted to carry from one roof to another, even if the residents of the houses did not establish an eiruv between them. The Sages did not prohibit carrying between roofs, as it is rare to transfer an item from one roof to another. However, it is only permitted to transfer objects between roofs provided that one roof is neither ten handbreadths higher nor ten handbreadths lower than the adjacent roof. This is the statement of Rabbi Meir. And the Rabbis say: Each and every one of the roofs is a domain in and of itself. It is permitted to carry from one to the other only if the residents of both houses established an eiruv.

Rabbi Shimon says: Roofs, courtyards, and enclosures are all one domain with regard to vessels that were inside them when Shabbat began, and one may therefore carry from one of these areas to another. However, they are not one domain with regard to vessels that were inside the house when Shabbat began and were later taken into one of the above domains. A vessel that was inside the house when Shabbat began and subsequently carried to one of these areas may be carried from one roof, courtyard, or enclosure to another only if an eiruv had been established between the domains.

GEMARA: Abaye bar Avin and Rabbi Ḥanina bar Avin were sitting, and Abaye was sitting beside them, and they sat and said: Granted, the Rabbis maintain: Just as residents are divided into separate domains below, and they may not carry from house to house without an eiruv, so are residents divided into separate domains above, on the rooftops, and it is prohibited to carry from one roof to another without an eiruv.

However, Rabbi Meir, what does he maintain; what is the rationale for his opinion? If he maintains that just as residents are divided into separate domains below, so are residents divided into separate domains above, why, in his opinion, are they considered one domain? And if he maintains that they are not divided into separate domains, as any place above ten handbreadths off the ground is considered one domain, even if a roof is ten handbreadths higher or ten handbreadths lower than the adjacent roof, it should likewise be permitted to carry from one roof to the other.

Abaye said to them: Have you not heard that which Rav Yitzḥak bar Avdimi said that Rabbi Meir would say: Any place that you find two domains, i.e., places set apart from each other by disparity in height or by boundaries, and yet they are halakhically one domain, for example, a pillar ten handbreadths high and four handbreadths wide situated in a private domain, it is prohibited to adjust a burden on one’s shoulders upon it, by rabbinic decree, due to the concern lest he come to do the same thing on a mound in the public domain. The legal status of a mound ten handbreadths high and four handbreadths wide located in a public domain is that of a private domain. In that case, it is prohibited by Torah law to transfer an object from the public domain to the mound. Here too, in the case of roofs, Rabbi Meir prohibited transferring objects between roofs with a height disparity of ten handbreadths, by rabbinic decree, due to the concern lest one come to transfer an object from the public domain to a mound in a public domain.

Abaye and Ḥanina bar Avin understood by inference from this ruling that in the opinion of Rabbi Meir, it would be prohibited to adjust one’s burden even on a mortar and even on a vat that were overturned in a private domain and that are large enough to constitute private domains in their own right.

Abaye said to them: The Master, Rabba, said as follows: Rabbi Meir spoke only in the case of a pillar or the raised base of a millstone. Since a person fixes a place for them they are comparable to a mound in a public domain in that they are rarely moved. However, the Sages did not issue a decree in the case of portable objects.

The Gemara raises a difficulty. There is the case of a wall that is between two courtyards, which is fixed, and nevertheless Rav Yehuda said: When you analyze the matter, you will find that according to Rabbi Meir all roofs form a single domain in and of themselves, and likewise all courtyards form a single domain in and of themselves, and all enclosures form a single domain in and of themselves. It is permitted to carry from one courtyard to another, although it is not permitted to carry from a courtyard to a roof.

What, is it not that it is permitted to move objects from one courtyard to another via a dividing wall, even though it is ten handbreadths high? This poses a difficulty to the opinion of Rabbi Meir, who prohibits the transfer of an object from one place to a place ten handbreadths higher or lower.

Rav Huna bar Yehuda said that Rav Sheshet said: No, that explanation is incorrect, as Rav Yehuda meant to say that according to Rabbi Meir it is permitted to carry in and carry out between one courtyard and another, or from one enclosure to another, via the openings between them. However, Rabbi Meir concedes that one may not transfer objects over the wall that separates the two domains, as the wall is considered a domain in and of itself.

We learned in the mishna: And the Rabbis say that each and every one of the roofs is a domain in and of itself. It was stated that amora’im disagreed about the following issue. Rav said: According to the Rabbis, one may move objects on each roof only within four cubits. As, according to the Rabbis, the legal status of roofs is like that of courtyards, in that it is prohibited to carry from one roof to another, and each roof is fully open to a domain into which carrying is prohibited. Therefore, it is also prohibited to carry objects farther than four cubits on each roof. And Shmuel said: It is permitted to move objects throughout each entire roof.

The Gemara comments: With regard to partitions that are conspicuous, i.e., detached houses whose walls are distinct, everyone agrees that it is permitted to carry throughout each roof. Where they disagree is with regard to partitions that are not conspicuous, i.e., attached houses, which appear as though they share a common roof although they are owned by different people.

Rav said: One may carry on each roof only within four cubits. Rav does not state the principle: Extend and raise the partitions between the houses below, which states that the walls of the houses are considered to extend upward and create partitions between the roofs. And Shmuel said: It is permitted to carry throughout each entire roof, as he states the principle: Extend and raise the partitions.

The Gemara asks a question based on that which we learned in the mishna: And the Rabbis say that each and every one of the roofs

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Eruvin 89a explores when eiruv agreements allow pouring water into shared courtyards and debates whether rooftops count as a single carrying domain on Shabbat.