While it's called Pompey's Pillar, it was actually raised in honor of Diocletian in 300 BCE. The column supposedly comes from the Temple of Serapis (now gone) as part of the facade. The temple (40 km to the west) was enormous, and held the 'daughter library' to the Bibliotheca Alexandrina. If the size of the column is any indication, the temple rivaled any in Rome.
There are three galleries here, where the Apis bulls were mummified and buried, but there are west of the ridge. There are a few sphinxes here, from differing periods, and the ruins of cisterns and underground chambers, but on the whole the site is jumbled. Instead of an actual excavation, it is more of an outdoor museum of bits and pieces from nearby temples and sites.