Sirmium

Sirmium was the Roman capital of the Lower Pannonia province. At the end of the 3rd century AD, it became one of the four capitals of the empire as a result of Diocletian’s reforms and was home to the Illyrian legions.

The remains of ancient Sirmium are incorporated into the Serbian city of Sremska Mitrovica on the banks of the Sava River, including an impressive visitor center. The city was destroyed by the Avar invasion in the late 6th century AD. In the 9th century, Sirmium became one of the centers of Saint Methodius, the founder of Slavic Christianity, who was active mainly in Moravia (present-day Czechia and Slovakia) but also in Pannonia along the Danube.