At the northeast corner of Constitution Gardens, this 1835 stone gatehouse is a remnant of the days when the Washington City Canal flowed through this area. The lock that transferred boats from the City Canal onto the C&O Canal, which begins in Georgetown, was located here and this building was where the lockkeeper lived until the lock was decommissioned in 1855. The building was undergoing restoration and possible relocation at the time of research; the completion date was unknown.