The Citadel, also known as the Fort of Cascais, was built in the 16th century by King Philip I to defend Cascais Bay. It enlarged an earlier, smaller stronghold and was also one of the forts built along the Tagus estuary to protect Lisbon. In 1807 it was occupied by General Junot during the Napoleonic invasion and in 1870, during the reign of King Louis I, became a royal summer palace. This lasted until the assassination of King Carlos I in 1908 and it is now the President’s summer residence. There is a small open air artillery museum in the garden.