Taking up an entire block on the eastern edge of the square is the Owens-Thomas House, considered to be one of the finest examples of English Regency architecture in the country. The home, with its columned entrance portico, brass inlaid staircase, and more, was designed by architect William Jay from 1816 to 1819 for cotton merchant Richard Richardson. The home is made largely of tabby—an indigenous, concrete-like material made of lime, oyster shells, and sand. The exterior is English stucco. The interior, which includes three rare built-in marble-top tables that belonged to the Richardsons, has many stunning features, including an entryway with a brass inlaid staircase and a drawing room with an unusual ceiling that makes the room appear to be round. The carriage house, also open for tours, is one of the earliest intact urban slave quarters in the South and opens into an English-inspired parterre garden.