What empire what ruled by King Darius 1?

In the 5th century BC, Darius 1, or Darius the Great ruled Persia. At the time, it was a true empire. He installed distributed governing, by dividing the country and assigning Satraps to rule the parts in his name. He also uniformed the monetary system, the language and he pretty much wrote the Imperialist 101. Clever chap, really.