Seleucus I clashed several times with his southern rival for power, the Ptolemaic Dynasty. The Ptolemaic Dynasty controlled most of Egypt and the lands around it, and would fight the Seleucid Empire on many occasions for control of Syria. Seleucus I conquered much of Anatolia, and was preparing to invade Macedonia, when he was assassinated. This momentarily put an end to the Seleucid Empire's ambitions in Greece. After Seleucus I died, his heirs spent much of their time and money trying to maintain the enormous empire they had inherited. In this, they were rather successful, but the vastness of the empire defied attempts by the successors of Seleucus to control it effectively.