via Boing Boing
Manhattan is just one of hundreds of metropolitan areas in the United States that has an eruv, which is a wire that symbolically turns public spaces into private spaces during the Jewish Sabbath.
From Mental Floss:
On the Sabbath, which is viewed as a day of rest, observant Jewish people aren't allowed to carry anything — books, groceries, even children — in public places (doing so is considered "work"). The eruv encircles much of Manhattan, acting as a symbolic boundary that turns the very public streets of the city into a private space, much like one's own home. This allows people to freely communicate and socialize on the Sabbath — and carry whatever they please—without having to worry about breaking Jewish law. Along with everything else in New York City, the eruv isn't cheap. It costs a group of Orthodox synagogues $100,000 a year to maintain the wires, which are inspected by a rabbi every Thursday before dawn to confirm they are all still attached.