The Fortezza (from the Italian word for “fortress”) is the Venetian-era citadel of the city of Rethymno in Crete.
In the aftermath of the fall of Cyprus to the Ottoman Empire in 1571, the Venetians began fortifying Crete, their largest remaining overseas possession. Construction began on 13 September 1573.
The fortress was conquered by the Ottomans in 1646, and remained in use until the early 20th century.
During Ottoman times, most of the space inside the fortress was settled, and the last houses were demolished only in the 1960s.
Large-scale restoration work is under way since the early 1990s.

Source: wikipedia