The castle, the heart of the city, is perched on a hillside. It was built by the Visigoths in the 5C, enlarged by the Moors in the 9C and modified in the reign of Alfonso Henriques. It was used as a royal residence from the 14 to the 16C. The castle's ten towers all provide viewpoints over the city. However, from the former parade ground just inside the outer wall, the view over the Tagus, the suspension bridge and the left bank is marvellous.