St Mawes Castle is the best preserved and most elaborately decorated of any of the coastal defence positions that Henry VIII constructed throughout his reign. The building was constructed in order to counter invasion attempts from the French and the Spanish navies and has a counterpart, Pendennis, on the other side of the Fal estuary. The castle fell to Parliamentarians in 1646 and was not properly re-fortified until the late 19th Century.