The construction of the Fortezza started in 1570 by the Venetian dominants of the island in order to protect the area of Rethymnon and the town from the imminent Ottoman threat. As it used to be in that period, the fortress has the shape of a star, with six bastions and three gates. At the center there was the Catholic church of San Nicolo, transformed to a mosque when the Ottomans took the fort.

The most important monuments of the Fortezza are:

The residence of the Councilors, an impressive two-storey building, ground floor and first floor, with many ample rooms, a "copy" of the Italian mansions of the Renaissance. Possibly it continued to be in use also by the Ottomans as residence of the Ottoman officials of the town.

The Rector's house should be an impressive complex of buildings as we can suggest from the few ruins visible today.

The Cathedral founded in 1583 and dedicated to San Nicolo. During the Ottoman domination it has been abandoned and the Ottomans transformed it to a mosque.

It is a big square building with a dome at the center. Only the base of the old minaret is maintained today.

The two powder kegs within the Fort. There are two domed rectangular buildings with a small ventilation hole. They have extremely thick walls with small doors and corridors in the interior so that the powder is well secured.

The Artillery storeroom is a two-storey building, with two arches. The upper storey had wooden floor supported by three wooden pillars; the entrance was decorated with an arched lintel. The building was used to store the canons, weapons and accessories of the artillery.

The so-called "Diocese mansion" , a complex of two buildings, named so because of its vicinity to the Cathedral. The bigger of the two buildings has an extended room with arches. The smaller one is possibly a construction added later to the main building.

No systematic excavations have been carried out in the Fortress up to now. Rescue work in the monuments and trial excavations have been carried out occasionally. A project of development of the whole space had been made by the eminent Greek architect D. Pikionis, but was never realised. Recently, the Municipality of Rethymnon attempts to develop and restore the place in order both to protect the monuments and use them for various modern activities