Since the Byzantine period, the city of Heraklion has been known as ‘Kastro’ because of the walls that surround it. In 824 AD, Crete was conquered by the Arab Saracens, who fortified the town with walls made of unfired mud bricks reinforced with goat and pig hair. The wide wall, and deep moat surrounding it, lent it the name, used for centuries, "Fortress of the Trench." In 961 A.D. Crete came under the control of the Byzantines, who built the fortress Rocca at Kanli Kastelli, and reinforced the fortifications around the city of Heraklion.  In 1206 the city was conquered by the Genovese, who also fortified the castle of Candia.  In 1217 Crete passed into the hands of the Venetians, who adapted and repaired the existing walls. After 1453, the Venetians build dozens of forts on the island. The current walls of Heraklion were begun in 1462 and their construction took more than a century. The city wall follows a triangular plan of ​​3 km and was an impregnable structure, while outside the wall smaller forts were built to reinforce it. The large castle was captured after 23 year siege by the Turks in 1669. The Turks repaired the walls, and adapted them to their needs, meanwhile changing their names. The fortress of Heraklion is considered one of the best preserved Venetian works in Europe.