Egypt after the Arab invasion of 640-2 was governed from the Delta of the Nile to the First Cataract by Arab governors deputed by the Khalif of Baghdad. The Christian Copts and Greeks were not materially interfered with, provided they paid their taxes regularly. In 706 Arabic finally displaced Greek as the official language of the country, and never subsequently lost its hold over Egypt. Coptic (the degenerate form of Ancient Egyptian) gradually sank into the position of a ritual language only connected with religious exercises and literature; and Arabic since the 8th century has been the universal speech of all Egypt, except in the Oasis of Siwa, where a Berber dialect is still spoken, and among the tribes inhabiting the lands between the Cataract Nile and the Red Sea, who preserve their Hamitic (Gala-like) languages. A good deal of Arab colonization of Upper and Lower Egypt, and of Nubia and Dongola, took place between the 8th and the 12th centuries. In 828-32 a serious rebellion of Copts and of malcontent Arabs was only suppressed by the Baghdad Khalif introducing an army of 2000 Turks; and from this time onwards the Turks had much to do with Egypt, as they had with Syria and Mesopotamia, because the Arabs were losing their energy and fighting capacity. After 856 most of the functionaries in Egypt were Turks; and in 875 a Turkish governor, Ahmad bin Tulūn, turned his governorship into a hereditary sovereignty. The Tulunid dynasty of sultans governed Egypt till 905, when the direct rule of the Baghdad Khalifs was resumed. Then, once more, a Turkish governor was appointed to rule Egypt for the Khalif, in 935, to whom was granted the kingly title of Ikshid. The Ikshids governed until 969, when they were supplanted by the establishment of the Fatimite Khalif Mu’izz-li-din-Allah already referred to, who left Tunisia in 973 to take up his residence first in Alexandria and then in newly-founded Cairo.