The Porta Nigra in Trier is the best preserved Roman city gate north of the Alps. This is thanks to an eremite monk called Simeon, after whose death the building was converted into a church. It retained that function for nearly 750 years. The superimposed church building was removed at the start of the 19th century, when efforts began to conserve and restore the Porta Nigra.
In 2012, during a preliminary investigation for planned remediation of the structure, the possibility arose for the DAI’s Architecture Section to examine the building more closely. Comprehensive drawings and maps were made as the foundation for all further analysis. Systematic and detailed mapping of the various features made it possible for reconstruction drawings to be produced for the first time of the phases of construction and use of the Porta Nigra, which were then displayed in 3D models as part of the project.
The surfaces and construction phases are mapped (Photo: B. Geißler, DAI) 
In situ drawing (Photo: B. Geißler, DAI)
The building’s eventful history can be seen in the gatehouse (Photo: B. Geißler, DAI) 
3D working model of the Porta Nigra in various phases: 2nd century AD, 17th century, today (Model: C. von Bargen, B. Geißler, DAI)