King's College London, UK 2020 was meant to be a relatively uneventful year in the global transition to a largely urban world. Half the world's population was already living in cities, projected to rise to two-thirds by 2050. The world's urban centre of gravity was moving, or rather returning, East. Moreover, in many parts of the world, a new type of urban structure had emerged-the polycentric mega-region: groups of cities in which populations and economic activities are linked over a wider geographical area, facilitated by improvements in transport (high-speed rail), technology (high-speed internet) and global connectivity (airports and seaports). But 2020 didn't follow the script. A global pandemic, on a scale not seen for a century and with echoes of earlier plagues, has upended established economic, social and physical norms, and seems to threaten the rise of the city. Are we now headed for a new Age of Dispersal-an era marked by lower population densities, lower rates of mobility-especially long-distance mobility-and the growing importance of smaller cities and towns? Over the last 30 years, an elite group of cities has thrived as key nodes of the global economy, attractors of talent, ideas and wealth in an ever-more-connected system. But in the last few months, we have glimpsed a looking-glass world where the very benefits of global cities-high degree of connectivity, density and agglomeration-have been found also to be vulnerabilities. Building on the work of Jean Gottmann (1961) in his study of the Boston-New York-Washington 'megalopolis', Peter Hall, working with Kathy Pain, defined the term 'polycentric mega-city region', and characterised it as arising from the long-term process of very extended decentralisation from big central cities to adjacent smaller ones, old and new (Hall and Pain, 2006). This process was accelerated by late 20th century regional developments in East and SouthEast Asia, in places like the Pearl River Delta and the Yangtze River Delta in China, the Tokyo-Osaka corridor in Japan and Greater Jakarta. Each city and town within the network is both its 'own place' and also part of a wider functional urban region, held together by 'dense flows of people and information carried along motorways, highspeed rail lines and telecommunications cables'.