The House of Refuge in Stuart, Florida, is the oldest building in Martin County constructed in 1876. It was part of a chain of such rescue stations along the East Coast of Florida and is the last one remaining. The keepers led lonely isolated lives, much like lighthouse keepers. They rescued shipwrecked sailors from Florida's treacherous shoals. The tower was added in 1942 as a lookout for German U-boats that torpedoed freighters. Today the House of Refuge is maintained by the Martin County Historical Society. It is located on one of the few rocky beaches in Florida. The rocks are part of the Anastasia Formation and are coquina, a sedimentary rock of sand and seashells. This was used by the Spaniards in forts like the one in St. Augustine as it withstood canon balls.