The development of the first urban centers is one of the most fundamental phenomena in the history of temperate Europe. New research demonstrates that the earliest cities developed north of the Alps between the sixth and fifth centuries BC as a consequence of processes of demographic growth, hierarchization, and centralization that have their roots in the immediately preceding period. However, this was an ephemeral urban phenomenon, which was followed by a period of crisis characterized by the abandonment of major centers and the return to more decentralized settlement patterns. A new trend toward urbanization occurred in the third and second centuries BC with the appearance of supra-local sanctuaries, open agglomerations, and finally the fortified oppida. Late Iron Age settlement patterns and urban trajectories were much more complex than traditionally thought and included manifold interrelations between open and fortified sites. Political and religious aspects played a key role in the development of central places, and in many cases the oppida were established on locations that already had a sacred character as places for rituals and assemblies. The Roman conquest largely brought to an end Iron Age urbanization processes, but with heterogeneous results of both abandonment and disruption and also continuity and integration.