C ities are epicentres of the COVID-19 pandemic. From Wuhan to Madrid to São Paulo, the scenes have been grim-wards bursting with patients, queues of refrigerated lorries acting as temporary mortuaries, food-bank lines snaking around empty streets. At the same time, people and animals have thronged streets and parks, while carbon emissions and smog levels have plummeted from New Mexico to Delhi. COVID-19 is still running its course. The immediate aftershocks-job losses, poverty, food scarcity-need addressing urgently. But much has been learnt. The experience is already motivating change. In May, mayors from 38 of the world's largest cities-including Hong Kong, Los Angeles in California and Durban in South Africaannounced a set of principles for redesigning their metropolises to be more sustainable and equitable. Combating climate change is one priority of the Global Mayors COVID-19 Recovery Task Force. Milan, Paris, Bogota Responses to the pandemic in India's slums, Brazil's favelas and Africa's marketplaces show that networks play a crucial part in making cities more resilient. Let's enhance and empower them. Health workers check the temperatures of people in the Dharavi slum in Mumbai, India, as part of coronavirus screening.