[AUSTRIA.NIEDER 03705] 'Roman Heidentor in Petronell-Carnuntum.' For centuries the Danube was the northern border of the Roman empire. Military strongholds along the river often grew into cities. The largest became Carnuntum, where the Amber Route, connecting the Adriatic with the Baltic, crossed the Danube. It had more then 50.000 inhabitants. Nowadays it's the largest excavation of Austria. Main sight is the Heidentor, a name that is wrong in two ways. It was not a gate and not heathen, but a double triumphal arch, erected for christian emperor Constantine II. Maquettes show how it looked in those days, so does a drawing on plexiglass, through which you can see the ruins of today. Photo Paul Smit.