We have learnt that to be defined as a רשות היחיד (private domain,) an area needs to be surrounded by walls or partitions, at least 10 טפחים (handbreadths) high or deep.

We have also seen that מדאורייתא (biblically), מחיצות (partitions) on 3 sides is sufficient, but that מדרבנן (rabbinically), the fourth side needs to be marked or partially enclosed, depending on its width and status.

One of the most practical questions regarding the partitions used for the eruv concerns whether the sea or a river can be counted as a partition on one or more sides.

One the one hand, the water level could be very close to the level of the land, without the required 10 טפחים per 4 אמות drop (תל המתלקט) required for a partition.

On the other hand, given that water is not solid matter, and the ground underneath it often does drop at this gradient, perhaps the gradient should be measured by that of the solid ground which a person wading through the water would be walking down.

We have found explicitly (Shabbos 100a) that if a pit 10 טפחים deep is filled with water, even if the water reached the walls of the pit, it is still considered to be its own private domain.

This seems to show that a valley or depression filled with water could still be considered its own domain so long as its banks or the ground underneath it has the required gradient, serving as its partitions.

It follows logically that if these banks or slopes act as barriers for a different domain, they should also act as barriers for the domain that they separate this different domain from.

Our daf discusses the case of a מבוי that was surrounded on one side by a garbage pile and the other side by the sea.

There is a debate amongst the Rishonim whether these two sides were along the length of the מבוי or along the narrower widths of the מבוי, which could have its own ramifications, but we shall assume for now that 2 sides were closed correctly and 2 sides relied on the garbage heap and sea as partitions.

The Gemara related that רבי (Rabbi Yehuda haNasi) did not wish to either permit or forbid carrying in this מבוי.

He declined to forbid it seeing as there were valid partitions at the end of the day, but did not wish to permit it either, because of two concerns:

1. The garbage might be removed leaving the one side without a partition.
2. The sea could “bring up שירטון”- recede leaving washup-up stones and sand along the banks, thus destroying the natural partition.

The Gemara then asks what the opinion of the רבנן (the majority of sages) is, and two versions of events follow:

1. רב יוסף בר אבדימי says that they forbid carrying in such a מבוי and Rav Nachman then rules like them.
2. רב יוסף בר אבדימי says that they permit it, but Rav Nachman rules against them.

According to both versions brought by the Gemara, Rav Nachman forbids carrying in this מבוי , and given the lack of debate amongst the Amoraim, it is likely that this will be the halacha.

One question still open is whether the רבנן forbade carrying in this מבוי for both reasons thatרבי was concerned about, or only for one of them.

Perhaps their main concern was that that the garbage heap, which the Gemara concludes was privately owned, might be removed, a very likely event, but the less likely concern about the sea receding and leaving an unenclosed and relatively flat area of stones along its shore would not be a reason on its own to forbid it.

Another important question in this case is whether we are dealing with the sea or ocean, or with a river or lake.

Although the word ים is used, and this term usually refers to the seas specifically as opposed to rivers (see for example Brachos 9/Mishna 1 re ימים ונהרות )the concern of שירטון might apply to both, depending on precisely how we understand it.

Furthermore, most of the main Torah centers in Israel and possibly all of those in Bavel were not on the ocean.

Whereas the case that רבי dealt with could have been by the sea- major rivers are not present in Israel, the next case the Gemara brings seems almost certainly to have involved one of the main rivers of בבל, where most of its main centers were situated.

The Gemara describes how the Amora מרימר closed off the alleys of the city of Sura with nets, so as not to rely on the ים, for the same reason that רבי was initially concerned about.

As Sura was along the Euphrates River and certainly not on the coast, it seems that the term ים in this sugya certainly must also be referring to major rivers.

We see precedent for this in Tanach where the round pool in Shlomo’s palace was referred to as a ים (Melachim I 7/23) and was referred to by Chazal (Eruvin 14a) as the ים שעשה שלמה.

It is also clear from this case that מרימר was not only concerned about the garbage being removed but also about natural changes in the seashore or riverbank.

As such, the chapter should end here, and we should conclude that the sea or a river may not be used as the boundary of an eruv, period.

However, it is not quite as simple as that, thankfully.

Rabbeinu Chananel appears to have a different גירסא (version of the text) of the Gemara. In his girsa, the second version of the Gemara has Chachamim permitting the מבוי and Rav Nachman ruling leniently like them. It also narrates how אמימר closed the alleys of Sura with nets and was NOT concerned about שירטון .

This seems self- contradictory as if there was no concern for שירטון, why would nets be required, and many Rishonim reject this version out of hand (see for example Rashba on the daf)

This permissive view is given more teeth, however, by the Rambam, who rule (Shabbos 17/5 ) that the sea may serve as a partition, and we are not worried about שירטון.

The Meiri on our daf also rules leniently.

Perhaps what was meant by Rabbeinu Chananel’s version of the Gemara is that מרימר closed alleys that were not open to the sea with nets, and allowed the alleys that were open to the sea to be treated as closed even without nets, as he was not concerned about שירטון .

There is another major sugya in the second chapter of this masechta(Eruvin 22b) that is extremely relevant to this discussion, which I hope to discuss when we get there.

Practically speaking, the Shulchan Aruch (O.C. 363/29) rules leniently like the Rambam, whereas the Rema rules stringently like the Tur, Rashi’s version of the Gemara and other stringent poskim.

However, even those who allow the sea or river to be used as a partition could have rather strict conditions , among them:

1. The gradient of the sea, river, or its banks has to be at least as steep as 10 handbreadths per 4 armlengths.
2. The gap between the מבוי and the sea or river may not be more than the 10 handbreadth limit ( a wide beach between the street and the ocean could thus invalidate the entire partition.)
3. The river cannot freeze solid during the winter (see Taz O.C. 363/20)

In addition, many Ashkenazi communities in Europe did use rivers as partitions for their Eruvin, and it thus seems that some of their authorities also held that the Gemara’s ban on using the sea or a river was not absolute, and depends on the circumstances.

As we have seen, this is a complex issue, and there is tons more to say, but one thing certain from this discussion is that anyone planning on relying on the sea or a river as an eruv boundary needs to know precisely what he is doing, or/and get guidance from someone who does!

These posts are intended to raise issues and stimulate further research and discussion on contemporary topics related to the daf. They are not intended as psak halacha.