The Iazyges were a nomadic Sarmatian tribe located in around where Romania, Ukraine, and Hungary meet today. They were a constant thorn in the side of the Roman Empire from the 1st Century BCE. They constantly resisted assimiliation and were among the last of the Dacian peoples to be quelled. In the late 1st Century CE, they crossed the Danube into Roman Pannonia and defeated Legio XXI Rapax (who were disbanded afterwards). It was only when Trajan took control of the Empire (and the war in Dacia) where the Iazyges were conquered. In fact, future emperor Hadrian was the one that forced them to submit. They were reduced to a client state of the Roman Empire after this (107 CE).

EDIT: Professor pronounced them (ee-uh-zee-gees)