Head 50km south from Sremski Karlovci and you’ll hit Sremska Mitrovica, site of the ancient Roman ruins of Sirmium. One of the four capitals of the Roman Empire, Sirmium was one of the largest cities in the world at its peak, a major Christian centre and a favourite haunt of Constantine the Great; no less than six Roman emperors were born here. Today, you can visit what remains of old Rome at the exceedingly well-maintained Imperial Palace complex.
