The citadel of Cascais was built approximately in 1488 by king Joao II. A small medieval fortress was not able to repel the Spanish troops led by the Duke of Alba, who in 1580 captured the village, and this conflict led to the unification of the Portuguese and Spanish crowns. Signed Iberian Union, and Philip II of Spain was proclaimed and crowned Portuguese king Philip I. During his reign, the fortress was rebuilt and turned into a typical citadel of the Renaissance.

In 1807, during the occupation of Portugal by Napoleon's troops, the citadel of Cascais was captured by the French led by General Junot, who remained in the village for some time. In the reign of king Louis II, from 1870 to 1908, one of the buildings of the citadel was used as a summer residence of the Royal family, and a small fishing village has become very popular after that. In 1878, by order of king Louis II in the citadel there was electricity. Thus, Cascais became the first city in the country, where there was electricity. The village began to expand and better roads to Lisbon and Sintra, many noble families built beautiful mansions on the coast. The infrastructure has improved, in 1889 the railroad was built. In 1896, king Carlos I posted in the citadel's first Oceanographic laboratory and personally conducted 12 scientific expeditions.

Today, the citadel has maintained its role as a summer residence for the President. The garden is open for visitors small artillery Museum under the open sky.