745. Uneven Alleys

Shabbos 17:20

If one of an alley’s walls is long and the other is short, the beam is placed by the short wall. When a pole is erected in the middle of an alley, it is permitted to carry in the section of the alley that is behind the pole but one may not carry in the section that is beyond the pole.

Shabbos 17:21

If an alley is twenty cubits wide (about 35 feet), one may enable carrying by erecting a wall ten handbreadths high and four cubits long (30” x 6’). This is the minimum measure of an alley. The wall is placed in the middle of the alley’s entrance, making it like two alleys, each with an entrance of ten cubits (15’). One might also leave a space of two cubits (3’) from one side of the alley and erect a wall three cubits long (4.5’), and leave a similar space on the other side of the alley with a similar wall. In this way, the entrance of the alley will be ten cubits wide (15’) and the sides will be functionally closed because the solid portions exceed the gaps.