The Heidentor of Petronell-Carnuntum from past to present
On the history and significance of the Heidentor since its construction in the 4th century
As part of the project "Twin it! — 3D for Europe’s culture", the State Collections of Lower Austria are digitising the Heidentor of Carnuntum as a symbol of Roman Austria in 3D. Not only is the current appearance made visible in 3D, but a total of four 3D models are being created. These are based on historical views, scientific knowledge, and current drone imagery.
From the ancient world to the present
The Heidentor of Carnuntum is one of the most significant cultural monuments in Austria and is well-known far beyond the country's borders. It is one of the few Roman monuments in Austria that has been continuously visible for nearly 2,000 years. Even in the Middle Ages and the Renaissance, the monument was mentioned in several travel reports. Many speculations about the builders and the function of the structure abound, which have not yet been fully clarified to this day. In the 13th century, it was believed that the Heidentor was the tomb of the giant Theuto. This regional legend originates from a Dominican chronicler who mentioned it in his Descriptio Theutoniae (“Description of the German Lands”) in the 13th century.
An initial description of the monument was written by the humanist Wolfgang Lazius in 1551. Wolfgang Lazius interpreted the Heidentor as a city gate. About 100 years later, the name "heydnisch Thor" appears for the first time, from which the current name is derived.
Stone robbery and restorations
In the 15th and 16th centuries, a significant amount of stone theft occured in Carnuntum due to a shortage of building materials, forever shaping the appearance of the Heidentor. Large ashlar stones were particularly suitable as sought-after material and were blasted out using black powder. The last two pillars were thus reduced to the inner core of cast masonry.
In the 18th century, the two English travellers Richard Pococke and Jeremias Milles recognised the Heidentor as a Roman structure. This also gave science an initial impetus to begin researching Carnuntum – a Pompeii outside the gates of Vienna – and to protect and preserve the monuments. The first to have restoration work carried out on the Heidentor at his own expense was the Schwechat industrialist Anton Widter in 1869.
The Heidentor visible today
The current appearance of the Heidentor was mainly shaped by renovation works in 1907. At that time, the lower pillar zones were encased, and the arch was covered. In the same year, the ruin passed into the ownership of the state of Lower Austria.
After further restorations on the surface of the pillars in 1957, the Heidentor was again extensively examined from 1998 to 2001 and preserved according to internationally valid standards of monument care.
The 3D model of the Heidentor
The 3D model of the present Heidentor was implemented using photogrammetry. A drone was used as a tool, taking photos from different angles and heights. The photogrammetric images create a three-dimensional digital representation of the current state of the Heidentor. The use of high-precision GPS systems (RTK) allows a model to be created with centimetre accuracy.
What is Photogrammetry?
To create a uniformly lit model, diffuse light (cloudy weather) is necessary when taking photos. Any shadows will also appear disadvantageously in the texture of the 3D model.
After the drone flight recordings and the compilation of images using photogrammetry, annotations were incorporated into the 3D model, enabling the location of ancient spolia within the Heidentor. Spolia are reused stone materials that originate from older Roman structures and were redeployed in the Heidentor for cost reasons, including altars, inscriptions, and architectural ornaments. In the 3D model of the Heidentor, five of these spolia are mentioned in the annotations.
Additionally, a figure of an archaeologist was implemented into the 3D model to clarify the scale.