Now Heliopolis contain the earliest temple obelisk still in its original position. The 20.7 m / 68 ft high red granite Obelisk of Senusret I of the XIIth Dynasty is at Al-Matariyyah part of Heliopolis.
It is now in Al-Masalla area of Al-Matariyyah district near Ain Shams district (Heliopolis). It is tall and weighs 120 tons or 240,000 pounds.
The city's Egyptian name (shown in hieroglyphs, right, transliterated ỉwnw), is often transcribed as Iunu (literally "[place of] pillars"), and was often written in Greek as Ὂν On, and in biblical Hebrew as אן ˀÔn and און ˀĀwen.
According to Diodorus Siculus Heliopolis was built by Actis, one of the sons of Helios and Rhode, who named the city after his father. While all Greek cities were destroyed during the flood, the Egyptian cities including Heliopolis survived. The chief deity of Heliopolis was the god Atum, who was worshipped in the primary temple, which was known by the names Per-Aat (pr-ˁ3t; "Great House") and Per-Atum (pr-ỉtmw; "Temple [lit. "House"] of Atum"). The city was also the original source of the worship of the Ennead pantheon, although in later times, as Horus gained in prominence, worship focused on the synchrentistic solar deity Ra-harakhty (literally Ra, (who is) Horus of the Two Horizons). During the Amarna Period, king Akhenaten introduced monotheistic or perhaps henotheistic worship of Aten, the deified solar disc, built here a temple named Wetjes Aten (wṯs ỉtn "Elevating the Sun-disc"). Blocks from this temple were later used to build the city walls of mediaeval Cairo and can be seen in some of the city gates. The cult of the Mnevis bull, an embodiment of the god Ra, had its centre here, and possessed a formal burial ground north of the city.
As the capital of Egypt for a period of time, grain was stored in Heliopolis for the winter months, when many people would descend on the town to be fed, leading to it gaining the title place of bread. The Book of the Dead goes further and describes how Heliopolis was the place of multiplying bread, recounting a myth in which Horus feeds the masses there with only 7 loaves.
Heliopolis was well known to the ancient Greeks and Romans, being noted by most major geographers of the period, including: Ptolemy, iv. 5. § 54; Herodotus, ii. 3, 7, 59; Strabo, xvii. p. 805; Diodorus, i. 84, v. 57; Arrian, Exp. Alex. iii. 1; Aelian, H. A. vi. 58, xii. 7; Plutarch, Solon. 26, Is. et Osir. 33; Diogenes Laertius, xviii. 8. § 6; Josephus, Ant. Jud. xiii. 3, C. Apion. i. 26; Cicero, Nat. Deor. iii. 21; Pliny the Elder, v. 9. § 11; Tacitus, Ann. vi. 28; Pomponius Mela, iii. 8. The city also merits attention by the Byzantine geographer Stephanus of Byzantium, s. v. Ἡλίουπόλις.
Alexander the Great, on his march from Pelusium to Memphis, halted at this city (Arrian, iii. 1); and, according to Macrobius (Saturn. i. 23), Baalbek, or the Syrian Heliopolis, was a priest-colony from its Egyptian namesake.
The temple of Ra was said to have been, to a special degree, a depository for royal records, and Herodotus states that the priests of Heliopolis were the best informed in matters of history of all the Egyptians. Heliopolis flourished as a seat of learning during the Greek period; the schools of philosophy and astronomy are claimed to have been frequented by Orpheus, Homer, Pythagoras, Plato, Solon, and other Greek philosophers. From Ichonuphys, who was lecturing there in 308 BC, and who numbered Eudoxus among his pupils, the Greek mathematician learned the true length of the year and month, upon which he formed his octaeterid, or period of eight years or ninety-nine months. Ptolemy II had Manethon, the chief priest of Heliopolis, collect his history of the ancient kings of Egypt from its archives. The later Ptolemies probably took little interest in their "father" Ra, and Alexandria had eclipsed the learning of Heliopolis; thus with the withdrawal of royal favour Heliopolis quickly dwindled, and the students of native lore deserted it for other temples supported by a wealthy population of pious citizens. By the 1st century BC, however, Strabo found them deserted, and the town itself almost uninhabited, although priests were still there.
In Roman times Heliopolis belonged to the Augustamnica province. Its population probably contained a considerable Arabic element. (Plin. vi. 34.) In Roman times obelisks were taken from its temples to adorn the northern cities of the Delta, and even across the Mediterranean to Rome, including the famed Cleopatra's Needle that now resides on the Thames embankment, London (this obelisk was part of a pair, the other being located in Central Park, New York) . Finally the growth of Fustat and Cairo, only to the southwest, caused the ruins to be ransacked for building materials. The site was known to the Arabs as ˁAyn Šams ("the well of the sun"), more recently as ˁArab al-Ḥiṣn. It has now been brought for the most part under cultivation, but the ancient city walls of crude brick are to be seen in the fields on all sides, and the position of the great temple is marked by an obelisk still standing (the earliest known, being one of a pair set up by Senusret I, the second king of the Twelfth Dynasty) and a few granite blocks bearing the name of Ramesses II.