The first 3D model was created after a watercolour by Rudolf von Alt. The watercolour shows the view of the Heidentor from the west, around the time of the grain harvest. The structure stands on a conical rubble mound. Immediately behind the south-western pillar, the large lintel block can be seen.

Both still standing pillars are already very thinned at the bottom, the southern one significantly more than the northern one, which well documents the peak of stone robbery. Stone robbery for building material, which occurred especially in the 15th and 16th centuries, shaped the appearance of the Heidentor forever.

At the top of the northern pillar, the cast masonry of the building core can be seen, while the southern pillar has a still preserved brick cladding at this point. Below, on the south pillar, a short piece of a cornice and four large, light blocks are visible. At the top, two stone blocks also protrude like consoles.

For the 3D digitisation, an additional watercolour based on the template by Jakob von Alt, the father of Rudolf von Alt, was used, which provided a corresponding template for the design of the eastern view side. This was a stroke of luck, as both depictions thus come from a (family) hand and the two different viewpoints anticipated many details for the 3D drawing.

Another 3D model was recreated from two lithographs following the restoration measures undertaken by Anton Widter.

The two lithographs show the walling up of the still standing stone structures after the initial conservation measures by Anton Widter, an Austrian industrialist and art collector.

Between 1843 and 1846, the first restoration and conservation measures were commissioned by Anton Widter on the Heidentor, which had become very endangered in its stability due to centuries of stone robbery. These were the first systematically conducted and privately financed conservation measures of a Roman stone monument in Austria. Anton Widter had the ancient pillar remains encased with supporting masonry. The exact extent of these measures was described in 1893 by Josef Dell, who also included sketches in his reports: 

“Masonry at the pillars, at the arch and the parts rising above it …” (—Josef Dell, Excavations in Carnuntum, AEM 16, 1893, pp. 156–176)

The pillar core was only encased on the outer sides, leaving the ancient masonry visible in the gateway.

By 1868, further restorations were necessary, as masonry had come loose on the west side of the south pillar and was in danger of falling. These were also commissioned and financed by Anton Widter.

On 5 June 1907, the Heidentor was ceded to the Federal State of Lower Austria, which from then on was responsible for the preservation of the Roman building. Already between August and October 1907, further extensive security measures were implemented.

In the course of these works, the foundations were exposed and the Heidentor was scaffolded to carry out repairs in the upper area. The encasing of the pillars, which had already been done in 1860, was massively improved and the debris mound in front of the Heidentor was excavated. During these works, the pieces of the circular pedestal in the middle were also unearthed and reconstructed. 

Since then, further security, restoration, and conservation measures have been carried out, which continue to this day. The campaign “Twin it! – 3D for Europe’s culture”, in which the State Collections of Lower Austria digitised the Heidentor of Carnuntum as a symbol of Roman Austria in 3D, has also contributed significantly to the preservation of the “Roman landmark in Austria”.