Colonial cities have dotted our narrative as points on the emerging map of imperial commodity extraction or as centres of transport and administration. In this chapter, the first to adopt a synthetic overview approach, our attention turns specifically to urban zones, their changing role in the emerging spatial and environmental history of empire, and the character of their built environments. Cities will also be a specific focus in discussing the environmentally linked disease of bubonic plague (Chapter 10). Cities transform, sometimes obliterate, nature in their immediate environments. Such urban concentrations have also acted as hinges for the broader process of environmental and social change across large swathes of land described in the first half of this book. Cities, as human creations, sometimes seem to have ‘broken from nature’. Yet the rise of many colonial cities was intimately connected with the changing relationships between people and nature in the regions they touched. We will argue that their environmental boot-prints were varied and hybrid in character, but in part moulded by specifically British planning and styles. British trade, shipping, and planning helped to plant the kernel of new cities across the globe. Of the fifty largest cities in the world by the early twenty-first century, fifteen had at least partial roots in the British Empire, and if US cities founded in the colonial period are included (New York, Boston, Philadelphia, and Washington), the total is nineteen. British imperialism may not, alone, have been ‘the greatest creator of towns’ but urbanism was surely one of ‘the most lasting of the British imperial legacies’. Nine of those fifteen are in areas of South Asia which fell under British control; three—Cairo, Lagos, and Johannesburg—are in Africa. Imperialism also contributed to the rise of British ports and manufacturing towns, and the growth of London. London was the largest city in the world at the height of the British Empire between the 1820s, when it overtook Beijing, and 1925, when it was overtaken by New York. Its population expanded from about 1.3 million in 1825 to a height of nearly 9 million around 1950.