Carnuntum first occurs in history during the reign of Augustus (6 AD), when Tiberius made it his base of operations as a Roman fort in the campaigns against Maroboduus (Marbod).
Significant Romanisation occurred when the town was selected as the garrison of the Legio XV Apollinaris before 14 AD. A few years later, it became the centre of the Roman fortifications along the Danube from Vindobona (now Vienna) to Brigetio (Ó-Szőny). According to Tacitus, the emperor Claudius ordered the governor of Pannonia "to have a legion with an auxiliary on the bank of the Danube" to protect the losers of a dispute between Germanic tribes (the Quadi and Marcomanni) and deter the victors from the temptation to invade Pannonia. To this period (about 50 AD) belongs the auxiliary castrum of a cavalry ala 1.5 km south-west of the legionary fortress.
The legion was sent to Syria and possibly Armenia by Nero in 62 or 63.
In 71 AD, after several campaigns, the Legio XV Apollinaris returned to Carnuntum and rebuilt its fortress. The legion fought in the Trajan's Dacian Wars the main body of the legion remained in Pannonia. In 115 war with Parthia broke out and the legion was sent to the east.
Legio X Gemina was sent to Carnuntum for a few years from about 63 AD. During the brief reign of Galba (68-69), it was transferred back to Hispania.
Legio VII Gemina, newly founded by Galba in 68 AD, was allocated to Carnuntum until about 71 AD after his defeat by Vespasian.
In 117/8 AD, Carnuntum became the permanent quarters of Legio XIV Gemina where it stayed for three centuries until the frontier collapsed in 430.
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 the capital of Pannonia Superior it was made a municipium by Hadrian (Aelium Carnuntum). 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 its 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 whose 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 (the conference of Carnuntum) 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 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.
The "Archaeological Park Carnuntum" comprises three sites:Museum, Heidentor and amphitheatre near Petronell
Excavations in the garden of Petronell Castle
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 4th 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" (pagan gate).
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.
In September 2011 aerial photographs and ground-penetrating radar led to the discovery of the typical contours of an ancient Roman gladiator school to the south of the Roman settlement, a ludus rivaling the Ludus Magnus school and covering an area of some 3,350 square yards (0.280 ha). This approach of aerial photography and modern remote sensing has allowed for a detailed virtual recreation of the gladiator school. The aerial photographs used in the recreation were acquired with a radio-controlled Microdrone md4-1000 quadrocopter, which captured a sufficient amount of photographs to create an overlap among them. Then, using a technique called Structure from Motion (SfM), a 3D model of the school was calculated using the sharpest images. The school, along with the amphitheater, was located outside of the town's walls. The school had training grounds, bathing facilities, an assembly hall and dormitories for the gladiators. The school also had a courtyard which housed a training area for gladiators. The school was attached to an open campus which was most likely used for chariot races.
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.
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.
In Frank Tallis' crime novel Vienna Blood both Guido von List and his novel Carnuntum appear, together with an eponymous opera based on the novel.