Koules is a Venetian castle and it was constructed from 1523 until 1540 in order to protect the port of Heraklion. During the Venetian era, its name was Rocca a Mare or Castello a Mare, while at the time of the Ottoman occupation, after 1669, the name changed to "Koules".
The area of the castle covers is 3.600 square meters. It has a quadrangle shape together with a semicircle part that provides strong protection on its east side. It includes two floors and the thickness of the walls is 8,7 meters. Francesco Basilicata on a review of 1630 says that on the ground floor of the fortification, there were 18 big canons, while on the second floor 25 smaller with different calibers, 300 boxes of gunpowder as well as 6.144 missiles of several sizes.
The protecting the monument of the flying lion of Saint Mark is carved on three different places of the tower. West of Koule is the boulevard Sofoklis Venizelos, where someone can walk by the sea, or enjoy fresh fish dishes, ouzo and wine in one of the local restaurants and tavernas.