(312 B.C.) The Seleucid Empire, based in Babylonia, is founded by Seleucus, former general over Alexander’s elite cavalry forces. Seleucus asserted control over Mesopotamia and all the lands conquered by Alexander to the east into the Indus Valley. After Seleucus, his empire would also expand westward into refers to the Roman providences in what is now Turkey. more Minor and the Levant.