The central building in the Aquis Querquennis fortification. Located at the intersection of the two main streets that lead in from the gates served as the Headquarters or Principia and is the administrative center of the fort. It was also a sacred place to a great extent.
Here they kept the banners of the Legio VII Gemina as well as imperial statues and the portraits of the emperors which presided over the public acts.
In its basilica the declamations and other public acts were carried out.