Grand Master Wignacourt commissioned the building of St Thomas Tower out of his own pocket, building it on a plot of land he had bought. It cost him 12,000 skudi, a huge sum for the time and is bigger than other towers built by the Order of St John.
The reason is that, apart from guarding the bay, it was also used for storing weapons. The eighteen-metre high tower, which was named after a small chapel dedicated to St Thomas, has four small bastions, one in every corner.
The walls are five metres thick and a wide dry ditch runs all round the tower. A small window in the basement looks over the front battery which was armed with cannons and faced the sea. The tower used to have a drawbridge.