HELIOPOLIS OF EGYPT. - Egyptian city, the ancient On (κον), capital of the 13th nome of Lower Egypt, sacred to the falcon-headed god Atum, creator par excellence, to whom the ichneumon, the phoenix and the bull Mnevis were sacred, the latter considered as his incarnation; Atum was soon afterwards identified with the solar gods in the syncretistic deity Atum-Ra and Harakhte, and included in the Heliopolitan ennead, of which he was the progenitor.
Around 2000 B.C. Amenemhat I (12th dynasty) raised to him a sumptuous temple on the ruins of a previous one; his son Senwosret I (the Sesostris of the Greeks) improved it. The temple soon became a center of priestly science; Strabo (XVII, 27-28) still visits there the chambers where Plato and Eudoxus were said to have been lodged, but he finds there above all the traces of Cambyses' devastations and notes by then the decadence of the ancient priestly science; he notes instead the presence of obelisks, one of which still survives (Arabic el-misallah) of Syene granite, more than 20 m. high, with a hieroglyphic inscription of Senwosret, placed on the occasion of the Sed festival, that is, of the jubilee; another obelisk fell in the 12th century; there now survive, beside the obelisk, ruins of the city 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, in Ex. 1, 17 as one of the cities built by the Israelites at the Pharaoh's command.
About 1 km south of the ruins of H., toward the south, in the direction of Cairo, there is today the village of el-Ma'jarijjah, where stands the so-called "tree of Mary", that is, a sycamore planted in 1672 and fallen in 1906; of it only one 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 spring still existing is said to have been made to gush forth by Jesus and is not salty like the others in the surroundings. And here there is now a chapel officiated by the Jesuits. Some apocrypha linger to narrate the sojourn of Jesus in Egypt, such as the so-called Gospel of Thomas and the Pseudo-Matthew; in them it is narrated among other things that Jesus would have entered a temple (of H.?) and would have performed prodigies there.