Greek name for the ancient Egyptian town of Iunu (biblical On). Modern day Heliopolis, a north-western suburb of Cairo, was built on top of many of the ancient monuments. As a result large parts of the site have never been investigated properly. Heliopolis once was the principal cult centre of the sun, hence the Greek name which means 'city of the sun'. Here the god was worshipped in several forms and under several names, such as Atum, Re-Harakhty and Khepry (and Aten during the reign of Akhenaten, who built a temple here). As Atum he was the creator god who commenced his work here, and became the founder of the Ennead of Heliopolis.
The first-known sun temple was built here, probably as early as the early Old Kingdom, and it is believed that this temple served as a model for the later sun temple of Niuserre at Abu Ghurob. Here there was a double temple, dedicated to Re-Harakhty and Atum. According to a Late Period inventory tablet, one of these temples had at least three courts and three pylons in front of a sanctuary called 'House of the Benben', in all probability an open courtyard containing the Benben stone. This stone had an irregular, conical shape and was a symbol of the primeval mound. It was believed that the rays of the rising sun touched this stone first. The name of the stone is derived from the Egyptian word 'weben', which means 'to rise'. The same is true of the benu-bird (a kind of heron, the Greek Phoenix), a manifestation of Atum, the god of Heliopolis. Historically speaking, the benben-stone was the predecessor of the obelisk and perhaps also of the pyramid and pyramidion. Many rulers erected obelisks in Heliopolis, some of which were later transported to other sites, such as the Caesareum in Alexandria from whence they were taken in modern times to London and New York, or Rome.