Tohoros 6:8

A basilica (a type of oblong hall) is a private domain vis-à-vis the laws of Shabbos and a public domain vis-à-vis the laws of ritual impurity. Rabbi Yehuda says that if a person standing at one door can see people entering and leaving through the other door, it is considered a private domain for both things. If not, it’s considered a private domain vis-à-vis the laws of Shabbos and a public domain vis-à-vis the laws of ritual impurity.

Tohoros 6:9

A forum (another kind of building, similar to a basilica) is a private domain vis-à-vis the laws of Shabbos and a public domain vis-à-vis the laws of ritual impurity; the same is true of its sides (which are used by people). Rabbi Meir says that the sides are considered a private domain for both things.