Carnuntum (Carnous, Καρνους, in Ancient Greek according to Ptolemy) was a Roman legionary fortress (castrum legionarium) and headquarters of the Pannonian fleet from 50 AD. After the 1st century, it was capital of the Pannonia Superior province. It also became a large city of 50,000 inhabitants. Its impressive remains are situated on the Danube in Lower Austria halfway between Vienna and Bratislava in the Carnuntum Archaeological Park extending over an area of 10 km2 near today’s villages of Petronell-Carnuntum and Bad Deutsch-Altenburg.
In Roman times Carnuntum had a history as a major trading centre for amber, brought from the north to traders who sold it in Italy; the main arm of the Amber Road crossed the Danube at Carnuntum.

As Aelium Carnuntum, the capital of Pannonia Superior, it was made a municipium by Hadrian. Its importance is indicated by the fact that Marcus Aurelius resided there for three years (172–175) during the war against the Marcomanni, and wrote part of his Meditations there. Also Septimius Severus, at the time governor of Pannonia, was proclaimed emperor there by his soldiers (193), to replace Emperor Pertinax, who had been murdered. In the Severan dynasty (193–235) Carnuntum experienced an economic boom, the canabae reaching their maximum size. Caracalla elevated it to colony status as Septimia Colonia Aurelia Antoniana. During the reign of Gallienus, the Pannonians rebelled by electing the usurper Regalianus, who established a mint with coins depicted him and his wife Sulpicia Dryantilla. He was killed shortly afterwards by his own soldiers, probably at Carnuntum.
In 308, during the Civil wars of the Tetrarchy, the Emperor emeritus Diocletian chaired a historic meeting there, the Conference of Carnuntum, with his co-emperors Maximian and Galerius, to solve the rising tensions within the tetrarchy. It brought about freedom of religion for the Roman Empire.

In 374, it was destroyed by Germanic invaders, the Quadi and Iazyges. Although partly restored by Valentinian I, it never regained its former importance, and Vindobona became the chief military centre. During the Barbarian Invasions, Carnuntum was eventually abandoned and used as a cemetery and source of building material for building projects elsewhere. Eventually, its remains became buried and forgotten.

Civilian city

The remains of the civilian city extend around the village Petronell-Carnuntum. There are several places to see in the city: Roman city quarter in the open-air museum, palace ruins, amphitheatre, and Heidentor.

The Roman city ruins are exposed in the open-air museum directly in the present village. One of the ancient houses, called the House of Lucius, has been rebuilt using traditional techniques. It was opened to the public on 1 June 2006. The forum was next to the palace ruins, also referred to as the large public baths.

Some way outside the city was a large amphitheatre, which had room for about 15,000 spectators. A plate with an inscription found at the site claims that this building was the fourth largest amphitheatre in the whole Roman Empire.

Between 354 AD and 361 AD, a huge triumphal monument was erected next to the camp and city. Contemporary reports suggest that Emperor Constantius II had it built to commemorate his victories. When the remains of Carnuntum disappeared after the Migration Period the monument remained as an isolated building in a natural landscape and led Medieval people to believe it was the tomb of a pagan giant. Hence, they called it Heidentor (‘Heathens’ Gate’ or ‘Pagans’ Gate’).

Fortress amphitheatre
The only remaining building of the fortress is an amphitheatre, located just outside the fortress. Today, a small adjacent museum shows the history of gladiators.

Museum Carnuntinum
The archaeological museum Carnuntinum, which is situated in the village of Bad Deutsch-Altenburg on the river Danube, exhibits important archeological finds from the ancient city.