Heliopolis is a suburb of Cairo about 10km from the city centre, which was built in the early part of the 20th century as a luxurious residential centre for Cairo's wealthy citizens. Virtually nothing remains of the ruins which lie beneath Heliopolis, once a great city and religious centre which spanned the whole of ancient Egyptian history.

The ancient city of Heliopolis, the city of 'On' in the Bible, was the chief town of the 13th nome of Lower Egypt. It has a long history and was dedicated to the sun-god Re and to Atum. In Egyptian mythology its name was Iunu, meaning 'pillar' and it was thought to be the 'mound of creation' from which the world arose. The 'pillar' refers to the ancient fetish which was worshiped at this most sacred place since earliest times. The status of the city was developed along with the solar cult of Re from at least Dynasty III and there are many references to the cults practised there in the Pyramid Texts of Dynasty V, whose kings were thought to come from Iunu. There are references to sanctuaries of the 'Ben Ben', the Sun God Re, the Phoenix and the Obelisk of Atum. Atum was the creator god of Heliopolitan cosmology who begot the first divine couple, Shu and Tefnut who in turn gave birth to Geb, the earth and Nut, the sky. Geb and Nut were the parents of Osiris, Isis, Seth and Nephthys and these nine gods made up the 'Great Ennead of Heliopolis' who together form a single divine entity.

Now buried beneath the sprawling modern city, the archaeological context of the ancient remains are difficult to interpret. We know that there was a religious construction dedicated by Djoser Netjerikhet of Dynasty III, whose stepped tomb at Saqqara was the prototype for the great pyramids to follow. Several fragments of very fine limestone relief were found in the temple area at Heliopolis excavated in 1903 by Schiaparelli. Now exhibited in Turin Egyptian Museum, the fragments show lines of text naming Netjerikhet and some of the gods of the Ennead, stressing the importance of the solar cult at that time. Other fragments of wall decoration which have more recently come to light suggest that the chapel seems to have been constructed to celebrate Djoser's jubilee ceremony which took place around Year 30 of his reign.

Many subsequent kings also built monuments at Heliopolis. The city was renowned for its large number of obelisks, a symbol of sun-worship which were still being erected there up to the Late Period. Today, its solitary reminder of greater times is a single obelisk of Senwosret I (Dynasty XII), the oldest obelisk in Egypt, which originally stood with its companion before a temple of Amun. Examples of obelisks have been found which were reused in other sites of the Delta region, as Heliopolis was slowly dismantled and its stone used in construction work at Memphis and later, Cairo. The city which the Greeks re-named Heliopolis was burned down by the Persian conqueror Cambyses and according to the Greek historian Strabo, was in ruins by 24 BC.

Since Schiaparelli's early exploration of the site, subsequent excavation work was carried out by the Egyptian Service des Antiquities and by Petrie in 1911 before the city reached the proportions we see today. The University of Cairo has undertaken systematic exploration of the area since 1976, confirming the huge size of the site which stretched beyond the boundaries of the temple area, as well as its importance as a centre of trade between Egypt and the Middle East and as an extensive religious centre.

The obelisk of Senwosret I is now in a park on the outskirts of Heliopolis at Mattariya. There are also a few small remains of other finds from Heliopolis in the park, including some granite column bases from a temple of Amenhotep III. Displayed in an open-air museum is a carved red quartzite naos of Tuthmose III from the Gebel Ahmar quarry and a number of other fragments. Other objects can be seen in a museum at the south-east corner of the park.

A new tomb belonging to Wadj-Hor, a palace worker of Dynasty XXVI, has recently been discovered in the residential area of Heliopolis. The tomb was found 10m below the surface of a building site and entered from the ground above, which is surrounded by other houses. Three vaulted chambers have been found which open into another vaulted room and in the debris there were 29 shabtis with the name of Wadj-Hor. In the southern chamber archaeologists under the direction of Zahi Hawass, have found three limestone sarcophagi. The tomb is currently still under excavation.

During 2006, excavating in the in the Ain Shams and Matariya districts of Heliopolis, archaeologists have uncovered parts of a large pharaonic sun temple. The Egyptian and German teams working together discovered the site beneath a market place known as Suq el-Khamis. Objects found include green paving stones from a temple floor, a pink granite statue, weighing four tonnes, thought to be Rameses II and another seated statue on which is inscribed the cartouches of Rameses II. There are plans to remove buildings in the area to conduct a more thorough excavation which may reveal much more of Heliopolis's ancient past.

Not far from the obelisk is an ancient sycamore, known as the Virgin's Tree (Shajjarat Maryam) which was planted in 1672 from a shoot of an older tree. The site is sacred to Coptic Christians, who believe that the Holy Family sheltered beneath it after crossing the desert. The tree was presented to the Empress Eugenie of France by Khedive Ismail, but she wisely left it where it was because it was a place of pilgrimage.

The small museum and park at Heliopolis is found at Midan el-Massala, which can be reached by taxi from Mattariya metro station on the el-Marg line from Cairo.