Rato Fort, also known as Santo António Fortress and Ilha das Lebres Fort, was ordered to be built during the reign of King Sebastião to protect the mouth of the Gilão rviver and the entrance to the port of Tavira. Later, in 1670, with the construction of the S. João Fort, Rato Fort took on a secondary role in defensive strategy.

However, the old fortress was refurbished, as its presence was essential to reinforce the line of fire of the new bastion. From the beginning of the 19th century, the number of soldiers stationed at the Rato Fort decreased, until the garrison became defunct in 1840.

Its military architecture is from the modern era. The fort is polygonal in shape with bulwarks at the corners, a cornice on the outside wall and a barracks inside the square with an arsenal and supply well.