736. Enclosing an Alley

Shabbos 17:2

In order to permit carrying in a closed alley (one that is enclosed on three sides), we must erect a vertical pole on the fourth side, or a horizontal beam over it. Either of these is considered to enclose the fourth side, making the alley a private domain, in which carrying is permitted. Under Torah law, one may carry in an area that is enclosed by only three partitions; enclosing the fourth side is a rabbinic enactment, so a pole or a beam is sufficient.

Shabbos 17:3

To permit carrying in an open alley (which is enclosed on two sides), we must erect an entry frame on one side and either a pole or a beam on the other side. An alley that is bent (rather than straight) is treated like an open alley.