Sesostris was the name of a legendary king of ancient Egypt who is suppossed to have led a military expedition into parts of Europe. The story originated in the writings of Herodotus.
According to Herodotus, Diodorus Siculus (who calls him Sesoosis), and Strabo, he conquered the whole world, even Scythia and Ethiopia, divided Egypt into administrative districts or nomes, was a great law-giver, and introduced a caste system into Egypt and the worship of Serapis.
Herodotus claims Sesostris was the father of the blind king Pheron, who was less warlike than his father.
Khyan, the powerful but poorly-documented Hyksos king of the Fifteenth dynasty of Egypt, whose prenomen was Seuserenre, is perhaps another possible prototype, for objects inscribed with his name have been found from Baghdad to Knossos.
Sesostris is evidently a mythical figure created to satisfy the pride of the Egyptians in their ancient achievements, after they had come into contact with the great conquerors of Assyria and Persia. When we recollect that the Nubian Taharqa of the 7th century BC, who was hopelessly worsted by the Assyrians, was credited by Megasthenes (4th century) and Strabo with having extended his conquests as far as India and the Pillars of Hercules, it is not surprising if the dim figures of antiquity were magnified to a less degree.
In the case of Taharqa, the miscellaneous levies which he employed himself and those which composed the Egyptian and Assyrian armies opposed to him, and the lands that Egypt and Nubia traded with, must all have been counted, partly through misunderstanding and partly through wilful perversion, to his empire.