The network structure of the urban revolution.

Long-distance interaction has deep prehistoric roots, but the networks that emerged during the Urban Revolution were unprecedented in scale and organization. How early cities sustained this extensive connectivity in the absence of formal markets or centralized states remains a fundamental question. Focusing on the Uruk Expansion in Mesopotamia (ca. 3900 to 3000 BCE), we assemble the largest spatial dataset currently available and reconstruct transportation networks across three successive phases. Using network analysis, we show that an initially dendritic, river-based system evolved into modular regional clusters and ultimately into a more integrated structure linked by selective long-distance shortcuts. This transformation reduced dependence on key intermediaries and generated small world-like patterns combining strong local cohesion with efficient system-wide reach. These results demonstrate that decentralized interaction processes, supported in part by mobile intermediary communities, played a central role in sustaining early urban connectivity.