HELIOPOLIS, an ancient city of Egypt (the Biblical On). It stood 5 m. E. of the Nile at the apex of the Delta. It was the principal seat of sun-worship, and in historic times its importance was entirely religious. There appear to have been two forms of the sun-god at Heliopolis in the New Kingdom—namely, Ra Harakht, or Re'-Harmakhis, falcon-headed, and Etom, human headed; the former was the sun in his mid-day strength, the latter the evening sun. A sacred bull was worshipped here under the name Mnevis (Egyp., Mreu), and was especially connected with Etom. The sun-god Re` (see EGYPT: Religion) was especially the royal god, the ancestor of all the Pharaohs, who therefore held the temple of Heliopolis in great honour. Each dynasty might give the first place to the god of its residence—Ptah of Memphis, Ammon of Thebes, Neith of Sais, Bubastis of Bubastis, but all alike honoured Re'. His temple became in a special degree a depository for royal records, and Herodotus states that the priests of Heliopolis were well informed in matters of history. The schools of philosophy and astronomy are said to have been fre quented by Plato and other Greek philosophers; Strabo, however, found them deserted, and the town itself almost uninhabited, although priests were still there. The Ptolemies probably took little interest in their "father" Re`, and Alexandria had eclipsed the learning of Heliopolis; thus with the withdrawal of royal favour Heliopolis quickly dwindled.
In Roman times obelisks were taken from its temples to adorn Rome and the northern cities of the Delta. Finally the growth of Fostat and Cairo, only 6 m. to the S.W., caused the ruins to be ransacked for building materials. The site was known to the Arabs as `Ayin esh shems, "the fountain of the sun," more re cently as Tel Hisn. It has now been brought for the most part under cultivation, but the ancient city walls are to be seen in the fields on all sides, and the position of the great temple is marked by an obelisk, and a few granite blocks bearing the name of Rameses II.