(In-)formal settlement to whom? Archaeology and old urban agendas for sustainability transitions in Ethiopia

African urban populations are growing predominantly through types of settlement commonly referred to as ‘informal’– settlements constructed outside the control of city or state governments. For the UN New Urban Agenda, informal settlement presents a challenge to developing sustainable cities. Settlement qualification in urban development discourse often relies on prescriptive formal models and considers anything not complying to these as ‘informal’ and unsustainable. This paper advances informal settlement as an adaptive response to Western planning models that builds on regional histories of organising urban space. Examining archaeological and historical urban records from northern Ethiopia, we define spatial patterns and social processes of urban transition over millennia. In the analysis, settlements that in current urban debates fall under the ‘informal’ rubric contribute to building urban resilience. A century-scale resolution reveals contingent conditions for cities enduring climatic and socio-political shifts during the Pre-Aksumite and Aksumite periods (c. 800 BCE–CE 900) and afterwards. Past urban transitions were marked by inverse settlement dynamics: as urban cores shrank, peri-urban settlement grew and new centres were established. Although spatial reconfigurations followed political shifts, urban settlement remained largely consistent: urban landscapes of food production, material processing, resource trading and ritual making. In the Aksumite record, informal processes convey flexibility and diversity of settlement forms to undergo sustainability transitions. The durability of urban morphologies in the archaeological record warrants against stereotyping informal settlement as a challenge to sustainability transitions. A long-term perspective supports emerging approaches to informal settlement today as a locally adaptive property of urban systems.