While Darius was preparing for another war against Greece, a revolt spurred in Egypt in 486 BC due to heavy taxes and the deportation of craftsmen to build the royal palaces at Susa and Persepolis. Under Persian law, the king was required to choose a successor before setting out on dangerous expeditions. When Darius decided to leave (487–486 BC), he (Darius) prepared his tomb at Naqsh-e Rustam (five kilometers from his royal palace at Persepolis) and appointed Xerxes, his eldest son by Atossa, as his successor. However, Darius could not lead the campaign due to his failing health and died in October 486 BC at the age of 64.