Koules, a building symbol of Heraklion, is a Venetian fortress built in the old Venetian harbor of Heraklion. Originally known by the Venetian names "Castello del Molo" and "Rocca a Mare", which meant "fortress in the sea", the current name “Koules” comes from the Turkish translation "Su Kulesi" of the Venetian name.

The first historical mention is in 1303 which states that there was a tower called "Castellum Comunis" which was destroyed by a major earthquake. From 1523 to 1540 built the building Koules, which had got reconstructions through the centuries, after continuous maritime disasters. The fort has two floors with an area 3.600t.m .. On the ground floor there were 26 apartments that used as warehouses and prisons, while upstairs there were residences of officers and guards. Historical reference of 1630 states that there were 18 cannons on the ground floor and 25 on the first floor. Inside the fort there were bakery, mill and water tanκ, which render autonomous the fortress under siege. During the Turkish occupation the building was used as a prison for Cretan revolutionaries.

Today Koules is used for art exhibitions, theatrical performances and various cultural events, and is a favorite visiting spot for walking for the residents of the city on sunny days.