On 7th November 1609 plans and a model of the projected tower were presented to the Order's Council. The proposal was accepted and the grand master himself attended a ceremony on 10th February 1610 at which the foundation stone was blessed and laid. The chosen date is supposed to have been the anniversary of the shipwreck of St Paul. The coast of the tower, 6748 scudi, 7 tari and 10 grani was borne by the Grand Master.
The design of the tower seems to have been by the Maltese architect Vittorio Cassar. Square in plan, it had a single stone-vaulted room on the ground floor and another above. The flat roof mounted a canon and could be used for lighting a bonfire and signalling at night. Four corner towers rise higher than the roof. The original entrance on the first floor was approached over a drawbridge from a flight of stone steps. These were removed in the 1950's when the road was widened. The ground floor entrance is a modern addition.