The tower was originally built in 1519 in the middle of the Tagus to defend the Hieronymite monastery and to serve as a lighthouse. Since the earthquake altered the course of the river, this five-storey Manueline tower now stands next to a beach. The Romanesque-Gothic structure is adorned with Venetian-style loggias and small domes like those in Morocco. Jutting out from the tower, facing the sea is a platform. On the ground floor, visitors will see the openings through which prisoners were thrown into the pits below.