Around 1000 BC, early fortifications were erected on the Festung Ehrenbreitstein hill on the opposite side of the Moselle. In 55 BC, Roman troops commanded by Julius Caesar reached the Rhine and built a bridge between Koblenz and Andernach. About 9 BC, the "Castellum apud Confluentes", was one of the military posts established by Drusus.
Remains of a large bridge built in 49 AD by the Romans are still visible. The Romans built two castles as protection for the bridge, one in 9 AD and another in the 2nd century, the latter being destroyed by the Franks in 259. North of Koblenz was a temple of Mercury and Rosmerta (a Gallo-Roman deity), which remained in use up to the 5th century.
With the fall of the Western Roman Empire, the city was conquered by the Franks and became a royal seat. After the division of Charlemagne's empire, it was included in the lands of his son Louis the Pious (814). In 837, it was assigned to Charles the Bald, and a few years later it was here that Carolingian heirs discussed what was to become the Treaty of Verdun (843), by which the city became part of Lotharingia under Lothair I. In 860 and 922, Koblenz was the scene of ecclesiastical synods. At the first synod, held in the Liebfrauenkirche, the reconciliation of Louis the German with his half-brother Charles the Bald took place. The town was sacked and destroyed by the Normans in 882. In 925, it became part of the eastern German Kingdom, later the Holy Roman Empire.
In 1018, the city was given by the emperor Henry II to the archbishop and prince elector of Trier after receiving a charter. It remained in the possession of his successors until the end of the 18th century, having been their main residence since the 17th century. Emperor Conrad II was elected here in 1138. In 1198, the battle between Philip of Swabia and Otto IV took place nearby. In 1216, prince-bishop Theoderich von Wied donated part of the lands of the basilica and the hospital to the Teutonic
