From Georges Posener, La Première Domination Perse en Égypte

When in Egypt … Dressed as the pharaoh, and thus as the incarnation of the Egyptian god Horus, the Persian emperor Darius (r. 522–486 B.C.E.) kneels before his “father,” the Apis bull, a living incarnation of Horus’s father, the Egyptian sun-god Osiris, at the top of this stone epitaph from Memphis. The Persian pharaohs of Egypt took part in the local religious rituals just as Egyptian rulers would. The epitaph records how the divine king Darius ceremonially conducted the god westward at an Apis bull’s funeral. The Egyptian priests recognized the Persian rulers’ willingness to participate in Egyptian worship as a sign that they were indeed the true rulers of Egypt.