Augustae was built as a fortified military camp in the mid-1st century, as the first fortification was made of wood and earth. The castle was naturally protected to the south by the Ogosta River, to the east and north by marshland. Access was possible only from the western side, where a fortified wall reinforced with a ditch was erected. In the 2nd-4th century Augustae developed as a Roman and an early Byzantine urban centre. Its total area reaches about 9 hа.
The fortress had the shape of an irregular pentagon extending from north to south. The fortress wall was dug inside up to 2.30 m and its thickness reached 2.50 m. Its walls were made of roughly worked stones, bonded with white mortar. The fortress had three gates - one to the west, north and east. The defence system consisted of protruding towers. The necropolis was located west of the fortress. Archaeologists have uncovered the fortification system of the Early Roman camp and the settlement dating to the Late Antiquity. The western wall with three rectangular towers and the western gate of the stone fortification have been explored. The site of the severely destroyed northern gate has also been established. Buildings have been uncovered in the inner part of the site, located in the approximate centre of the early Roman camp. In the 3rd–4th century the city was restored periodically after the invasions of the Goths. The last destructive invasion by the Avars in the 6th century marked the end of its existence.
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.