This fortress was built from 1573 till 1580 by the Venetians, for the protection of the inhabitants by the Turkish threat. It is starshaped with three gates and six bastions. In the middle, the church of St Nicolo, was turned into the Mosque of the Sultan Ibrahim Han. There were the Commander' s house, the Counsellor' s house, barracks, stables, ammunition - storehouses, a cistern and houses which were later destroyed. There was no systematic excavation on the site. From time to time, there were some excavatory attempts, when the actual buildings were being repaired.
Some years earlier, the 13th Ephorate of Byzantine Antiquities effectuated works of restoration and consolidation. The architect D. Pikiones had completed a study concerning a new project of the fortezza: a theatre for representations of the medieval cretan plays, tourist accomodations etc. Today the Municipality of Rethymnon in collaboration with the competent services, suggests a restoration study which will bring the monument to its full advantage. The most important monuments and architectural complexes are:
- The Counsellors' residence. It is formed of a ground floor and a first floor with large rooms. It was an imposing building, and served during the ottoman occupation, as an official residence. The Italian Remaissance palaces served probably as the model for its construction. - The Rector' s residence. It was an imposing complex. Today in ruins. The Cathedral. It was founded in 1583 and dedicated to St Nicolas. During the Ottoman occupation, it was laid waste and turned into a mosque of Sultan Ibrahim. It is a large square room with a cupola. The only remnants of it are the minaret' s base and the mihrab.
- Gunpownder-shorehouses. Inside the fortress there are two gunpowder-storehouses: They are rectangular buildings with vault and air-locks. The walls are thick with small doors and extra rooms for better safety. - Ammunition-storehouse. The ground floor and the first floor are covered with vaults. Over the entrance of the ground floor there is an arched lintel. Three pillars supported the wooden floor of the first floor; there, several parts of guns were stored. - Possible Bishop' s Mansion. It is formed of two buildings: The larger, is a unified room covered with vaults, while the smaller is a latter addition. It is considered as the Bishop' s Mansion because of the Cathedral near by.
During Venetian occupation the mosque Neratzes, which today is used as a music school, was the Augustinian church of the Holy Virgin. In 1657 the Turks transformed it into the mosque Gazi Housein or Neratze, and in 1890 they added a large minaret with two galleries, which was built from the famous stones from the village of Alfa. The chapel of the Holy Virgin, situated at its west side and dedicated to the Body of Christ, was also transformed into a seminary. Outstanding elements of this building are the doorframe and the three domes.
From 1300, Rethymno's harbour was constantly being changed and re-built to make it safer and hold more boats. Due to the prevailing currents along the coast, this was never entirely successful. It retains its picturesque character even today.