Dating back to the Greco-Roman Period, the Serapeum is located in the western section of the Necropolis of Saqqara. Close to the Serapeum lies the Greek Philosophers Circle, which contains statues of Plato, Heraclites, Pythagoras and Pindar. The Serapeum was located in 1851 by Auguste Mariette. It comprises impressive catacombs where the sacred bulls of Apis, the living image of Ptah (god of Memphis, and one of Ancient Egypt's national Gods) were buried in huge granite sarcophagus. A bull was also believed to be the incarnation of the blessed soul of Osiris after his death. All through its life it was treated as a deity with its own priests and a harem of cows. The bull was lain in a sarcophagus which could weight up to 80 tons, and a new sacred bull was selected. There are 24 sarcophagi found there, each one of which is a single rock weighting between sixty and eighty tons. The Serapeum was also used by dignitaries and princes as a tomb, people seeking the holy presence of the divine powers.