If you’ve ever strolled through historic neighborhoods in cities like Boston, Charleston, or Philadelphia, you might have spotted a curious feature under the front steps of old rowhouses—a bricked-up arch or a small chamber tucked beneath the stoop. These aren’t just random quirks; they’re called stoop vaults, and they reveal a fascinating piece of urban history from the 18th and 19th centuries, when homes were designed with clever solutions for everyday needs.