By 1870, Cascais had lost its strategic importance for the defence of the Lisbon coast and the River Tagus estuary and the citadel was no longer required for military purposes. King D. Luís adapted the old house of the governor to a vacation residence. The Royal Family popularised sea bathing and their presence in Cascais in September led to the Portuguese nobility also building houses in the town so they could be close to the King. The practice of Royal Family visits continued under King Dom Carlos until his assassination. King Carlos dedicated himself to the study of the oceans, installing in the Citadel the first Portuguese marine biology laboratory. Following the 5 October 1910 revolution and the end of the monarchy the palace was assigned to the Presidency of the Republic and used as a residence by several presidents.