Annu, or Heliopolis in Greek, is where the Great Ennead arose. Heliopolis translates to "City of the Sun", which is quite suitable since it was home of the cult of the Sun God Ra.
The two main centers of religion in ancient Egypt were Heliopolis and Memphis.
Hermopolis and Thebes are also important religious centers, and all four of these cities had their own version of the creation myth. The most popular one, the one we discussed here, is the one from Heliopolis...
The meaning of the word Ennead is a group of nine. In this case, it's a group of the nine oldest Gods of ancient Egypt: the Gods of the creation myth, with either Atum or Ra at the head.
Atum is the older version. When Ra was introduced as the creator of the universe, he was said to have taken the form of Atum.
So, according to the creation myth stated in the Pyramid Texts, Ra created himself out of the dark waters then proceeded to create Shu and Tefnut. When he was done, he wept; his tears then became the mortals of the Earth.
And that was how man was created according to ancient Egyptian mythology.
Shu and Tefnut procreated Geb and Nut - who in turn reproduced Osiris, Isis, Seth and Nephthys. These gods and goddesses together created the world as the ancient Egyptians knew it.
Heliopolis was the religious capital for the worship of the Sun God Ra. It had an impressive temple of Ra, a prestigious college and a library.
Legend has it Plato himself studied for a while at the college there!
There were obelisks and fountains; statues, shrines, and lakes.
It is said that Mother Mary bathed her son in the fountain of the temple at Heliopolis.
What I do know for sure is it's the site of what is called "The Tree of Virgin Mary" - where she took rest during her journey through Egypt.