Are composite walls effective? TB Eruvin 93

To enclose an area in order to make it a private domain, one needs walls that are least ten tefakhim tall. The Gemara on today’s daf TB Eruvin 93 discusses whether a composite wall fulfills the bill. The first understanding of Rav Ḥisda’s position is no. The wall cannot be a composite one. “An embankment, a height disparity between two surfaces of five handbreadths, and an additional partition of five handbreadths do not join together to form a partition of ten handbreadths, the minimum height for a partition to enclose a private domain. It is regarded as a partition of ten handbreadths only if the barrier is composed entirely of the embankment or if it is composed entirely of a partition.”(Sefaria.org translation) Based on an objection from a baraita, Rav Ḥisda’s position is modified.

“If there were two courtyards, one above the other, and the upper one was ten handbreadths higher than the lower one, or if it had an embankment of five handbreadths and a partition of five handbreadths, the two courtyards are considered separate domains and they establish two eiruvin, one for each courtyard, and they do not establish one eiruv. If the height disparity was less than ten handbreadths, the two areas are considered a single domain, and they establish one eiruv and they do not establish two eiruvin.

“Rav said: Rav Ḥisda concedes that an embankment and a partition combine with regard to the lower courtyard, since it faces a wall of ten, i.e., there is a full partition of ten handbreadths before its residents.” (Sefaria.org translation) More difficulties and solutions by redefining the case are further discussed on the daf. The bottom line of our original case is the composite wall consisting of the embankment and the partition equaling ten tefakhim high creates a private domain for the lower level which can be unify with an eruv, while the upper level cannot be joined with the lower level nor have its own eruv. But of course, there are dissenting views.

This conversation ends with a strange story and a pasak halakha. “Mareimar taught: An embankment of five handbreadths and an additional partition of five handbreadths above it combine to form a partition of ten handbreadths. Ravina met Rav Aḥa, son of Rava, and said to him: Has the Master taught anything with regard to this partition, whether it is effective or not? He said to him: No.[1] The Gemara concludes: The halakha is that an embankment of five handbreadths and a partition of five handbreadths combine to form an effective partition of ten handbreadths.” (Sefaria.org translation) The Shulkan Arukh codifies this conclusion. (Orekh Hayyim, 362:2)

 

---

[1] Perhaps the purpose of this story is to teach us that the simplest and most common sensible opinion, a composite wall is a wall. There was no need for such a discussion to entertain Rav Ḥisda’s innovation (חידוש).