The fort of Mardyck was constructed in 1622 by architect Jean Gamel. It was built for the Spanish who ruled Flanders at the time. The fort was captured, lost, and captured again by the French between 1644 and 1658. After the Battle of the Dunes (June 14, 1658) the fort came under the control of the English Commonwealth, in accordance with the terms of their involvement. After having bought Dunkirk and the fort of Mardyck from the English in 1662, King Louis XIV of France ordered that the fort be dismantled. On 12 February 1867, a French imperial decree established Fort-Mardyck as an independent municipality.
The arms of Fort-Mardyck are blazoned : Gules, unicorn saliant argent, on a chief a sun in her splendour, all within a bordure Or. (The emblazon shows a per fess field, which would make more sense, rather than a field and chief...)