The borders of modern France closely align with those of the ancient territory of Gaul, inhabited by the Gauls, a Celtic people. Gaul was conquered by the Romans in the first century BC, and the Gauls eventually adopted Romance speech and culture. Christianity also took root in the second and third centuries AD. Gaul's eastern frontiers along the Rhine were overrun by Germanic tribes in the fourth century AD, principally the Franks, from which the ancient name of "Francie" derived. The modern name "France" derives from the name of the feudal domain of the Capetian Kings of France around Paris (see now Île-de-France).