They are first mentioned by Roman sources in the third century. In the 4th century, they were among the peoples incorporated into the Hunnic Empire, within which they formed one of the most important parts. After the death of Attila, the Gepids under their leader Ardaric, led an alliance of other peoples who had been in the empire, and defeated the sons of Attila and their remaining allies at the Battle of Nedao in 454. The Gepids and their allies subsequently founded kingdoms on the Middle Danube, bordering on the Roman Empire. The Gepid Kingdom was one of the most important and long-lasting of these, centered on Sirmium, and sometimes referred to as Gepidia. It covered a large part of the former Roman province of Dacia, north of the Danube, and compared to other Middle Danubian kingdoms it remained relatively un-involved with Rome.