Maassluis was founded circa 1340 as a settlement next to a lock (in Dutch: "sluis") in the sea barrier between the North Sea and Rotterdam. Originally "Maeslandsluys", it was part of Maesland. In 1489 the settlement was sacked. During the Eighty Years' War, Philips of Marnix, lord of Sint-Aldegonde, started to build a defense wall but before its completion, the Spanish captured it in 1573 and Philips of Marnix was taken prisoner. A year later Maeslandsluys was looted by mutinous Spanish troops.