Sirmium entered the history in the course of the last decades of the old era with the arrival of Roman legions, but the founders of the town (civitas) were the Pannonian Amantins and Celts, as inhabitants of the pre historical Sirmium. As a Roman settlement, Sirmium developed very rapidly and in the period of the Flavian dynasty (69 – 96 of our era) the town was granted the status of a colony.