Heliopolis (i.e. City of the Sun), in Egyptian On, one of the oldest and most sacred cities of Egypt; was situated about 10 m. N. of Cairo, on the eastmost branch of the Nile; it was the centre of Egyptian learning; Solon and Plato are said to have studied there, and Potiphar was one of its chief priests; the famous obelisk Pharaoh's Needle stands near; and Cleopatra's Needle, now on the Thames Embankment, was originally of this city. Also the name of Baalbec.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Heliography * Helios