The first archaeological excavations in Sirmium began in 1957, at the Imperial Palace (Archaeological Site 1a). The site was discovered accidentally during construction of an apartment building on that location. Work was initially stopped temporarily, then permanently when massive walls, a system of radiant heating and floor mosaics were uncovered. The later discovery of the Roman circus (a hippodrome in the Greek-speaking part of the Empire) immediately adjacent to the palace provided conclusive evidence to identify the structure as an imperial palace.
The palace-circus architectural complex is one of the most important archaeological discoveries in Sremska Mitrovica. It was built at the end of the third or beginning of the fourth century in the southeast, elite section of the city, along the Sava river. A new city defensive wall protected this part of the city.
Imperial palaces in the Roman empire had formal spaces for the emperor’s administrative functions (the official part) and also private quarters where the emperor and his family lived (the residential part). The circuses built right next to the palaces represent the official structure for the ceremonial presentation of the ruler to his people. Chariot (bigae, quadrigae) races, the most popular sport in the ancient world, were held in the circuses. Roman circuses are known from all over the Empire, but the Sirmium circus is the only one discovered so far in Serbia.
On the archaeological site today only part of the imperial palace complex can be seen. The walls and pavements preserved there represent for the most part the residential quarters of the palace. Evidence of the luxurious interior decoration there is provided by the fragments of frescoes, mosaic pavements and architectural ornament in various kinds of stone which were imported from different parts of the empire: Egypt, Asia Minor, Greece, Italy. Installations for a radiant heating system were uncovered beneath almost every floor in the palace. The long duration and frequent use of the palace are documented by the numerous structural repairs, mosaic pavements in several levels and the large quantity of archaeological artifacts recovered.