The Thracians, one of the three primary ancestral groups of modern Bulgarians, appeared on the Balkan Peninsula some time before the 12th century BC. The Thracians excelled in metallurgy and gave the Greeks the Orphean and Dionysian cults, but remained tribal and stateless. The Persian Achaemenid Empire conquered parts of present-day Bulgaria (in particular eastern Bulgaria) in the 6th century BC and retained control over the region until 479 BC. The invasion became a catalyst for Thracian unity, and the bulk of their tribes united under king Teres to form the Odrysian kingdom in the 470s BC. It was weakened and vassalized by Philip II of Macedon in 341 BC, attacked by Celts in the 3rd century, and finally became a province of the Roman Empire in AD 45.