Under Cyrus and the subsequent Persian king Darius the Great, Babylon became the capital city of the 9th Satrapy (Babylonia in the south and Athura in the north). It was a centre of learning and scientific advancement. In Achaemenid Persia, the Babylonian arts of astronomy and mathematics were revitalised. Babylonian scholars made maps of constellations. The city was the administrative capital of the Persian Empire. This empire was the most powerful of the then known world. Many important archaeological discoveries have been made that improve our understanding of that era.