Stone Arch Dam at Jones Falls.
When it was built in 1831 this was the largest dam in North America and the third largest in the world.
At Jones Falls, boats rise and fall almost 60 feet via a set of four canal locks, and a dam, nicknamed the Whispering Dam, which holds back the 60 feet of water. The dam is approximately 360 feet long (107 m), 60 feet (18 m) feet high, and 27 feet (8 m) thick at the base. It was built with large sandstone blocks that were hauled by horse-teams to and shaped on site. No mortar or cement was used in this dam. The blocks were set in a giant arch, with the pressure of the water behind the dam pushing the perfectly-dressed blocks together, like an arch used in building structures.