The oldest archaeological finds in Susteren date from prehistoric times. For example, it turned out that in the district "In de Mehre" there must have been a settlement from the Iron Age. It may have been preceded by settlement during the Bronze Age. From the Roman period (after the beginning of the era) various finds have been made in Susteren and the surrounding area. In the fifties of the 20th century, a Roman cemetery was found on the north side of the medieval core of Susteren. A settlement from the transition from the Late Roman period to the Early Middle Ages has been excavated at Holtum, located west of Susteren. During the excavation of the medieval abbey in 1991-1993, finds from the Iron Age and Roman period were also made. It mainly concerns pottery shards that were found in the stream that flowed past the abbey. The estate donated by Pepin to Willibrord in the 8th century may date back to a Roman villa. However, traces of the buildings of a villa have not been found. During the excavation remains of the abbey were found in the form of traces of wooden buildings (8th/10th century), foundations of stone buildings (11th/19th century), wells, cesspits, ovens and more than a hundred burials (8th/11th century) . The monastery was located on the north side of the Sint-Amelberga Basilica, which, like the monastery, was first dedicated to Salvator. The oldest monastery is related in plan to 7th and 8th century monasteries from Northumbria (Jarrow, Monkwearmouth), the area from which Willibrord came. The Salvator Patrocinium is also carried by a church in Utrecht founded by Willibrord.