The fortification, built by the Muslims during the eleventh century, was the last defensive stronghold for the elite who lived in the citadel. After the conquest of Lisbon, on 25 October 1147, by Dom Afonso Henriques, the first king of Portugal, and until the early sixteenth century, Castelo de S. Jorge experienced its golden period as the centre of the court. When Portugal came under the Spanish Crown in 1580, the Castelo de S. Jorge took on a more military character, which it maintained until the start of the twentieth century.

It was during the twentieth century that the castle, the remains of the former royal palace, the Islamic alcazar and the experiences of the past were rediscovered. The restoration work which took place from 1938-40 accentuated its present majesty, rescued from the demolition work in progress, which can be seen here and there in the fragments of past construction work frequently documented in written sources.

At the end of the twentieth century, the archaeological works undertaken in various areas significantly contributed to ascertaining the age of the occupation of the hill top and confirm the priceless historical value which formed the basis for the Castelo de S. Jorge being classified as a National Monument, through Royal Decree of 1910.