Until the westward retreat in the first 324 years, Alexander conquered about 5 million square kilometers in 13, and established a great empire from Greece and Macedonia in the west, the Indus Valley in the east, the first waterfall of the Nile River in the south and the Syr Darya River in the north, making Macedonia the largest country in the world at that time. He died in Babylon 323 years ago at the age of 33. After Alexander's military conquest, ancient Greek civilization was widely spread and prospered, and the close cultural and economic exchanges between the East and the West opened the Hellenistic era.