Leith was one of Scotland?s principal ports, and was independent from the City of Edinburgh until 1920. Clerk shows a variety of boats in the harbour, possibly sheltering from the storm clouds approaching from the East. The rough sea and menacing sky have been painted with thick brushstrokes of dark wash. The round building at the edge of the harbour is the Signal Tower, built in 1686 by Robert Mylne. Originally it was a windmill, used to extract oil from rape-seed. In 1805, the sails and domed roof were replaced with a parapet, from which flags were flown as signals to ships.