but only one of them, that between the islands of Tombos and Abadin, remains navigable. Here Thutmosis built, under invocation of the gods of Heliopolis, one of those brickwork citadels, with its rectangular keep, which set at nought all the efforts and all the military science of the Ethiopians: attached to it was a harbour, where each vessel on its way downstream put in for the purpose of hiring a pilot.* The monarchs of the XIIth and XIIIth dynasties had raised fortifications at the approaches to Wady Haifa, and their engineers skilfully chose the sites so as completely to protect from the ravages of the Nubian pirates that part of the Nile which lay between Wady Haifa and Philse.* * The foundation of this fortress is indicated in an emphatic manner in the Tombos inscription: "The masters of the Great Castle (the gods of Heliopolis) have made a fortress for the soldiers of the king, which the nine peoples of Nubia combined could not carry by storm, for, like a young panther before a bull which lowers its head, the souls of his Majesty have blinded them with fear." Quarries of considerable size, where Cailliaud imagined he could distinguish an overturned colossus, show the importance which the establishment had attained in ancient times; the ruins of the town cover a fairly large area near the modern village of Kerman. Henceforward the garrison at Tombos was able to defend the mighty curve described by the river through the desert of Mahas, together with the island of Argo, and the confines of Dongola. The distance between Thebes and this southern frontier was a long one, and communication was slow during the winter months, when the subsidence of the waters had rendered the task of navigation difficult for the Egyptian ships. The king was obliged, besides, to concentrate his attention mainly on Asiatic affairs, and was no longer able to watch the movements of the African races with the same vigilance as his predecessors had exercised before Egyptian armies had made their way as far as the banks of the Euphrates. Thutmosis placed the control of the countries south of Assuan in the hands of a viceroy, who, invested with the august title of "Royal Son of Kush," must have been regarded as having the blood of Ra himself running in his veins.* * The meaning of this title was at first misunderstood. Champollion and Rosellini took it literally, and thought it referred to Ethiopian princes, who were vassals or enemies of Egypt. Birch persists in regarding them as Ethiopians driven out by their subjects, restored by the Pharaohs as viceroys, while admitting that they may have belonged to the solar family.