Saint Nicholas Fort is located at the end of an ancient mole in Mandraki area, inside the harbour of Rhodes. It is the first fortified tower a traveller will meet when entering the harbour. Due to its strategic position it was subject to the most brutal attacks during both sieges, as whoever could capture this Fort would more or less gain control of the harbour.
It was originally constructed as a relatively small round tower of a diameter a little wider than 17 meters in 1465 by Grand Master Pedro Raymondo Zacosta and was adorned with a relief of Saint Nicholas (patron Saint of the sea travellers) and the Coats of Arms of Master Zacosta and the Duke of Burgundy who had financed the construction.
The Tower was severely damaged during the siege of 1480 but was restored and fortified with a solid outwork (bastion) by Master Pierre d’ Aubusson, who finally converted it into a powerful fort. A small chapel in favour of St. Nicholas had also been built inside the protective bastion.