Shoal Tower National Historic Site is a circular stone defensive tower located on a shoal in the harbour, directly offshore from the site of the historic City Hall and the site of the former Market Battery in Kingston Ontario. From this location, the Shoal Tower had a commanding field of fire over Kingston’s commercial harbour and the entrance to the Rideau Canal. Official recognition refers to the tower itself plus the submerged rubble and cribbing associated with the tower’s construction.