Carnuntum Carnuntum ( Καρνους in Ptolemy ) was a Roman army camp on the Danube in the Noricum province and after the 1st century the capital of the Upper Pannonia province . Its remains are situated in Lower Austria halfway between Vienna and Bratislava on the " Archaeological Park Carnuntum " , extending over the area of 10 km² near today ' s villages Petronell - Carnuntum and Bad Deutsch - Altenburg . History . Carnuntum originated as a Roman army camp . Its name is nearly always found with " K " on monuments , and is derived from Celtic " karn - " ( " cairn " ) . Its name first occurs in history during the reign of Augustus ( 6 AD ) , when Tiberius made it his base of operations in the campaigns against Maroboduus ( Marbod ) . Significant Romanization occurred when the town was selected as the garrison of the Legio XV " Apollinaris " . A few years later it became the centre of the Roman fortifications along the Danube from Vindobona ( now Vienna ) to Brigetio ( Ó - Szőny ) . Under Trajan or Hadrian , Carnuntum became the permanent quarters of Legio XIV " Gemina " and the capital of Upper Pannonia . Even in Roman times it had a history as a major trading center 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 . It was made 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 " there . 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 308 the Emperor emeritus Diocletian chaired a historic meeting with his co - emperors Maximian and Galerius in Carnuntum to solve the rising tensions within the tetrarchy . It brought about freedom of religion for the Roman Empire . 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 . 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 were covered by decaying plant material . In fact the walking level is now 1 . 5 metres higher . Today . The " Archaeological Park Carnuntum " comprises three sites : Civilian city . 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 , has been rebuilt using traditional techniques . It was opened to the public on 1 June 2006 . The centre ( forum ) of the civilian city was next to the palace ruins , also referred to as the large public bath s . 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 4th largest amphitheatre in the whole Roman Empire . Heidentor . 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 " ( pagan gate ) . Military city . The only remaining building of the military city is an amphitheatre , located just outside of the fortified military camp . Today , a small adjacent museum shows the history of gladiator s . Gladiator school . In September 2011 aerial photographs and ground - penetrating radar led to the discovery of the typical contours of an ancient Roman gladiator school rivaling the Ludus Magnus school and covering an area of some . 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 . In fiction . Völkisch author Guido von List was so impressed with the ruins that he based his first novel on the subject . Another novel , " Household Gods " , by Harry Turtledove and Judith Tarr , is set in Carnuntum during the reign of Marcus Aurelius .