It was also a very old market for the amber brought to Italy from the north; the main arm of the Amber Road crossed the Danube at Carnuntum. It was created a municipium by Hadrian (Aelium Carnuntum). Marcus Aurelius resided there for three years (172-175) during the war against the Marcomanni, and wrote part of his Meditations. Septimius Severus, at the time governor of Pannonia, was proclaimed emperor there by the soldiers (193). In the 4th century, it was destroyed by Germanic invaders. Although partly restored by Valentinian I, it never regained its former importance, and Vindobona became the chief military centre. Carnuntum was finally destroyed by the Hungarians in the Middle Ages.
The remains of the civilian city extend around the village Petronell-Carnuntum. There are several places to see in the civilian city: Roman city quarter in the open-air museum, palace ruins, amphitheatre, and "Heidentor".
The Roman city quarter was a peripheral part of the former civilian city. The ruins are exposed in the open-air museum directly in the present village. One of the ancient houses, called The House of Lucius, is being rebuilt using traditional techniques. It was opened to the public on 1 June 2006.
The center (forum) of the civilian city was next to the palace ruins, also referred to as large public baths.
Some way outside the city was the large amphitheatre, which had room for about 15,000 spectators. A plate with an inscription at the place claims that this was the 4th largest amphitheatre of the whole Roman Empire.
The huge "Heidentor" (Heathens' Gate) was erected between 354 AD and 361 AD as a triumphal monument for Emperor Constantius II.
The only remaining monument of the military city is its amphitheatre. It was located just outside of the fortified military camp. Today, a small adjacent museum shows the history of the gladiators.