"Dozens of these stone enclosures—open at the top, usually square or circular, with a gap secured by a gate—remain scattered across New England. They were once a ubiquitous feature in the region. In fact, they were so necessary to the orderly functioning of a community that they were required by law. They were town pounds.More at the always-interesting Atlas Obscura.
In 17th-century America, livestock were generally not fenced in as they are today. Back in England, grazing animals were guarded by herders. But in the New World, where labor was scarce, animals like sheep and cattle were turned loose to graze on common lands instead. (The town green, or common, was often used for this purpose.)
If an animal strayed and was found wreaking havoc on private property, it was brought to the pound, where it was corralled with other wayward creatures and watched over by a town-appointed “pound-keeper” (sometimes called a “pound-master,” or “pounder”) until its owner could retrieve it—for a fee...
Today perhaps a hundred town pounds remain across New England. (They exist in other areas too. In addition to having mapped two dozen of New England’s pounds, users of the site waymarking.com have located one in a Nevada ghost town, and several in the U.K.)"