Little is known about Sirmium in the period from the death of Theodoric the Great (526) to Justinian’s war against the Ostrogoths (535). So far the simplest and most obvious method of analysing the surviving written sources, i.e. literal interpretation, has not been used for reconstructing the history of this city. Instead, for unclear reasons, it is almost commonly accepted that in 530 the city was attacked by the Gepids. The Ostrogoths supposedly repelled the enemy and their future king, Vitiges, distinguished himself in the battle. However, on the basis of the written sources (Cassiodorus and Procopius of Caesarea), a completely different reconstruction of the events is possible. It is more likely that there were two wars for Sirmium between the Gepids and the Ostrogoths: the first one in 526-527 and the second in 533-534. An examination of the historical context confirms that these two conflicts could have been consistent with other events and, just as importantly, enables us to explain the Ostrogoths’ complete inactivity in the face of the Frankish invasion.