Today, concern about population displacement triggered by climate change is prompting some sovereign states to tighten security measures, as well as inciting ethically and politically motivated calls to relax border controls. This paper explores resonances between the current climate predicament and events in the mid-Holocene. Paleoclimatic and archaeological evidence is reviewed suggesting that an abrupt turn to cooler, drier weather in the 4th millennium BCE triggered high volume migration to fertile river valleys – most fully documented in Mesopotamia but also visible in other regions around the world. This unprecedented agglomeration of bodies has been linked to the emergence of intensive irrigated agriculture and the rise of city-states. In conversation with the ancient Sumerian Gilgamesh epic, the paper draws upon archaeological research to conceptualize urban wall building and emergent practices of graphical notation as different forms of mediation. Both city walls and early writing, it is argued, deal with the interplay of mobilism and sedentarism, and both `media’ entail tactile, plastic use of local materials - namely riverbank clay. The paper addresses the paradox that the underpinning of `civilization’ by these once experimental media may now be fundamentally restricting socio-political, cultural, cognitive and embodied capacities to engage effectively with climate-driven upheaval.