The major landmark of Carnuntum today was originally a triumphal arch in front of the civilian city walls.
Located about 900 meters to the south of Carnuntum’s civilian city, the Heathen’s Gate was presumably erected during the reign of Emperor Constantius II (351–361 AD). The Heathen’s Gate was once a quadrifrons, a type of ancient Roman monument of cubic shape held up by four piers with an archway on each of the four sides. Each side of the cube measured 14.5 meters. The massive plinth in the middle of the structure blocking the passageways indicates that it was a triumphal monument. . A larger-than-life statue of the emperor probably stood on the plinth, which is about 4.3 meters high.