=140.= At the same period with the invasion, a Twelfth Egyptian Dynasty, the Osortasidæ, arose at Thebes, and became one of the most powerful tribes of native rulers. They obtained paramount authority over the kingdoms of Elephantine and Heracleopolis, held the Sinaitic Peninsula, and extended their victorious arms into Arabia and Ethiopia. Sesortasen I ruled all Upper Egypt. Under the second and third sovereigns of that name the kingdom reached its highest prosperity. The third Sesortasen enriched the country by many canals, and left monuments of his power at Senneh, near the southern border of the empire, which still excite the wonder of travelers. The largest edifice and the most useful work in Egypt were executed by his successor, Ammenemes III. The first was the Labyrinth in the Faioom, which Herodotus visited, and declared that it surpassed all human works. It contained three thousand rooms; fifteen hundred of these were under ground, and contained the mummies of kings and of the sacred crocodiles. The walls of the fifteen hundred upper apartments were of solid stone, entirely covered with sculpture. The other work of Ammenemes was the Lake Moëris. This was a natural reservoir formed near a bend of the Nile; but he so improved it by art as to retain and carefully distribute the gifts of the river, and thus insure the fruitfulness of the province. =141.= A weaker race succeeded, and the calamities of Lower Egypt were now extended throughout the land. The Hyksos advanced to the southward, and the fugitive kings of Thebes sought refuge in Ethiopia. With the exception of the Xoites, intrenched in the marshes of the Delta, all Egypt became for a time subject to the Shepherds. They burned cities, destroyed temples, and made slaves of all the people whom they did not put to death. Two native dynasties reigned at Memphis, and one at Heracleopolis, but they were tributary to the conquerors.