Cascais Citadel was built around 1488 by King Juan II. A small medieval fortress was unable to repel the Spanish troops led by the Duke of Alba, who in 1580 captured the village and the armed conflict has led to the unification of the Spanish and Portuguese crowns. Was signed Iberian Union, and Philip II of Spain was proclaimed and crowned as Portuguese King Philip I. During his reign, the castle was rebuilt and turned into a stronghold of the typical Renaissance.

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

Today, the citadel also retained the role for the President's summer residence. The garden is open to visitors is a small museum of artillery in the open air.