In the course of Julius Caesar’s conquest of Gaul and the ensuing Roman settlement of the lands on the Rhine’s left bank, there also followed the founding of Vicus Baudobriga (also Bodobriga or Bontobrica) on the way into the Mühltal (valley). The name is of Celtic origin, which implies that there had been Celtic settlement before the Romans came, or perhaps that there was one at the same time as the Romans were there. With the expansion of the Limes, the Middle Rhine lost its strategic importance. On the other hand, the river was gaining more and more importance as a supply and trade avenue. In the mid 3rd century, the Rhine’s right bank had to be evacuated and conceded to the Germani, thereby making the Rhine the Empire’s border once more. In 355, Roman Emperor Julian stopped the Germanic invasion and began securing the Middle Rhine. His successor Valentinian I finished the work. It was also at this time that the Late Roman castrum, the Römerkastell Boppard on the Roman road through the Rhine valley, was built. Towards the end of 405, the last Roman troops were withdrawn to defend Italy. The town’s next documentary mention did not come until the Early Middle Ages. According to this source from 643, Boppard was a Frankish royal estate and an administrative centre of the Bopparder Reich (a Merovingian state).