Rava’s teaching (see daf 6a), which allows for walls that are considered significant with regard to sukka to be perceived as sufficient for creating a reshut ha-yahid – a private domain – on the Shabbat of Sukkot, is applied by him to a number of inverse cases, as well. He teaches that in both the case of mavoy she-yesh lo lehi (an alleyway that has a sidepost) and the case of pasei bira’ot (an area surrounding a well that is partially closed off by four right-angled walls in each corner), partitions that are sufficient to create a reshut ha-yahid for Shabbat can be used as walls of a sukka, even though they do not meet the normal criteria of sukka walls.
The case of pasei bira’ot is a method of fencing off the area of the well or water-hole with four right-angled walls in response to the needs of olei regalim – pilgrims headed to Jerusalem for the holidays of Pesaḥ, Shavu’ot and Sukkot. In this case, the walls are so poorly designated that it was only the desire to assist people involved in this mitzva that led the Sages to permit their use. Since the olei regalim invariably brought with them animals for sacrifices in the Temple, there was a desperate need to make water as readily accessible as possible. During the times of year that the masses are commanded to travel to the Temple in Jerusalem, the only available water is in cisterns that collected rain water or wells.
The Jerusalem Talmud brings a dispute among the amora’im on the question of who is allowed to make use of these pasei bera’ot and carry within them on Shabbat. According to one opinion, such walls can only be used as an eiruv by olei regalim. A second opinion argues that the ruling was made with the olei regalim in mind, but during the times of year when people are oleh regel, anyone – even those not coming to Jerusalem – can benefit from them. The third opinion agrees that the special leniency was approved by the Sages with the olei regalim in mind, but argues that once it was adopted, the ruling works for all, and anyone can use the water in these wells.