In 1556, the Astrakhan Khanate was conquered by Ivan the Terrible, who had a new fortress built on a steep hill overlooking the Volga. In 1568 the Grand Vizier Sokollu Mehmet Paşa, who was the real power in the administration of the Ottoman Empire under Selim II, initiated the first encounter between the Ottoman Empire and her future northern rival. The results presaged the many disasters to come. A plan to unite the Volga and Don by a canal was detailed in Constantinople and in the summer of 1569 a large force under Kasim Paşa of 20,000 Turks and 50,000 Tatars were sent to lay siege to Astrakhan and begin the canal works, while an Ottoman fleet besieged Azov.