In 1249–1254, Koblenz was given new walls by Archbishop Arnold II of Isenburg; and it was partly to overawe the turbulent citizens that successive archbishops built and strengthened the fortress of Ehrenbreitstein that still dominates the city.
The city was a member of the league of the Rhenish cities which rose in the 13th century.
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-elector of Trier after receiving a charter.
The name Koblenz originates from Latin (ad) confluentes, confluence or "(at the) merging of rivers". 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.
It remained in the possession of his successors until the end of the 18th century, having been their main residence since the 17th century. In 1198, the battle between Philip of Swabia and Otto IV took place nearby.