Conferred with a Unesco World Heritage listing in 1998, this charming rural town and living museum rather thrillingly lies above one of the most complete, unexcavated Roman sites in Europe. And there's plenty to see above ground too, including a medieval basilica with a spectacular Roman-era mosaic floor and frescoed crypt, a nationally important archeological museum and the scattered remains of the Roman port.
Colonised in 181 BC, Aquileia was once one of the largest and richest cities of the Roman Empire – at times second only to Rome – with a population of at least 100,000 at its peak. After the city was levelled by Attila's Huns in AD 452, its inhabitants fled south and west, founding Grado and then Venice. A smaller town rose in Roman Aquileia's place in the early Middle Ages, and with the construction of the present basilica, it proceeded to become the largest Christian diocese in Europe.