Throughout the wild highlands and war-torn plains of Afghanistan and Central Asia lie traces of the ancient world. It was here, 2,300 years ago, that icon Alexander the Great became the first European to rule the East. In a major turning point in history, he crossed into Asia in 334 BCE, crushed the Persian Empire, and discovered a highly developed eastern civilization. In a six-part series, David Adams explores the footprints of an ancient world, today almost entirely erased.