 Another important center was Abydos, where the early rulers built large funerary complexes.During the Old Kingdom, the priesthoods of the major deities attempted to organize the complicated national pantheon into groups linked by their mythology and worshipped in a single cult center, such as the Ennead of Heliopolis which linked important deities such as Atum, Ra, Osiris, and Set in a single creation myth.Meanwhile, pyramids, accompanied by large mortuary temple complexes, replaced mastabas as the tombs of pharaohs.