Situated on the eastern section of the walls, Porta Pretoria provided the main access to the city of Augusta Praetoria. It was built in 25 BC after the defeat of the Salassians by Terenzio Varrone. It had three openings, which are still visible today: the central one for carriages and the side openings for pedestrians. The area inside the openings was used as a troop parade court, in its southern section, the land was dug up as far as the level of the ground during the Roman era.
On the outer facing openings you can still see the grooves from where the gates were lowered at night. The eastern facade still has some of the marble slabs that once covered the entire monument, on the inside it consists of blocks of puddingstone. In the Middle Ages there was a chapel dedicated to the Most Blessed Trinity resting against Porta Praetoria (now only an alcove of this remains), for many centuries, the same Porta Praetoria went by its name.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.