In the middle of the attractive Danube landscape, in the area of present-day Petronell, once the Roman metropolis Carnuntum was located. Today, the ruins of this ancient city are the largest archaeological park of Austria, with the so-called Heathen Gate as its showpiece. Of the former magnificent building only the arch of the gate survived. It was a pillar construction with four alleys, built from 354 to 361 AD as a triumphal monument for Emperor Constantius II.