The Sarmatians were a large Iranian confederation that existed from the 5th century BC to the 4th century AD. The Sarmatians originated in the central Eurasian Steppe, and they began migrating westward during the 4th and 3rd centuries BC, coming to dominate the Scythians by 200 BC. By the 1st century AD, they lived from the Vistula River and the mouth of the Danube eastward to the Volga and the Black Sea. At that time, they began to encroach upon the Roman Empire's territories, allying with the Germanic tribes. In the 3rd century AD, the Goths broke their dominance on the Pontic Steppe, and, during the Hunnic invasions of the 4th century, the Sarmatians joined the Goths and Vandals in settling in the Western Roman Empire. The Sarmatians were eventually decisively assimilated as Slavs in Eastern Europe.