HELIOPOLIS OF EGYPT. - Egyptian city, the ancient On (𓇾𓈖), capital of the 13th nome of Lower Egypt, sacred to the hawk-headed god Atum, creator par excellence, to whom were sacred the ichneumon, the phoenix, and the Mnevis bull, considered as his incarnation; Atum was subsequently soon identified with solar gods in the syncretistic divinity of Atum-Re-Harakhty, and included in the Heliopolitan ennead, of which he was the progenitor.
Ca. 2000 B. C. Amenemhet I (12th dyn.) erected a sumptuous temple to him on the ruins of a previous one; his son Senusret I (the Sesostris of the Greeks) improved II. The temple soon became a center of priestly science; Strabo (XVII, 27-28) still visited rooms there where Plato and Eudoxus were said to have been lodged, but he found there above all traces of the devastations of Cambyses and by then observed the decline of ancient priestly science; he noted instead the presence of obelisks, one of which still survives (Arabic el-misallah) in Syenite granite, over 20 m. high, with a hieroglyphic inscription of Senusret, erected on the occasion of the Sed festival, that is, the jubilee; another obelisk fell in the 12th century; today, next to the obelisk, ruins of the city survive and, 5 km away, a necropolis. In the Bible On is mentioned five times: first in Gen. 41, 45-50 and 46, 20 as the homeland of Joseph's father-in-law, and in Ex. 1, 11 as one of the cities built by the Israelites by order of Pharaoh.
Ca. 1 km south of the ruins of E., towards the south, in the direction of Cairo, is the modern village of el-Matariya, where the so-called "tree of Mary" stands, i.e., a sycamore planted in 1672 and fallen in 1906; of it only a single green branch remains.
Legend recounts that the Holy Family lived here during the exile and that the Virgin Mary with the child Jesus rested here in the shade of the plant: a still-existing spring is said to have been made to gush forth by Jesus and is not salty like the others in the surroundings. There is now a chapel here served by the Jesuits. Some apocrypha dwell on narrating the stay of Jesus in Egypt, such as the so-called Gospel of Thomas and the Pseudo-Matthew; in them it is recounted, among other things, that Jesus entered a temple (of E.?) and performed prodigies there.