One of Europe’s oldest towns (settled since 5000 BC), Sremska Mitrovica was once Sirmium – one of the Roman Empire's four capitals and, at its peak, one of the largest cities in the world. Six Roman emperors were born here, and it was a favourite haunt of Constantine the Great. You can visit what remains of old Rome here: excavated mosaic floors, rooms, baths and ancient heating systems are on display, as is a fascinating scale model of Sirmium.
The Museum of Srem, a short walk from the Imperial Palace ruins, displays numerous archaeological findings from Sirmium, including a unique Roman sundial with the sculptures of Atlas, Heracles and Ifikles.
Sremska Mitrovica is 50km south of Sremski Karlovci.