During Shabbat, observant Jews are not allowed to carry anything outside their home. Not even apartment keys, children, or medicine. But there's a loophole: a courtyard is considered part of one's home. So entire cities here are surrounded by a symbolic fence—an eruv—and declared a communal courtyard, to which the restriction no longer applies.

Tel Aviv is divided into several large zones (map) within which you can move around.

But just putting up a fence isn't enough. You need to make sure it stays in good condition. So every Friday before Shabbat begins, a special team drives around the eruv to check that nothing has broken. If something's wrong, it needs to be fixed before the first star appears, otherwise the eruv won't be valid.

By the way, this exists not just in Israel, but also in cities with large observant communities. For example in New York or Moscow.