The Venetian Fortezza fortress is built on the "Paleokastro" hill, located on the west side of the city. On the same hill the Acropolis of the ancient city of Rithymna was located, along with a sanctuary dedicated to Goddess Artemis. The carvings found in several parts of the hill indicate the existence of the acropolis. The settlement was probably located near the portside. However, there are not enough remains to inform us about the settlement's structure or the acropolis and the sanctuary.

The fortress was built during the Venetian period, and was founded on September 13 of the year 1573. It is a pentagonic construction built to confront enemy attacks. The fortress compound is still preserved in its original form and structure. Its total length is 1307 meters and includes four bastions (St. Lucas, St. Elias, St. Paul, St. Nicolas) and three peaks (Holy Spirit, St. Ioustinis, St. Sozontos).