The opening of Astley’s Amphitheatre on the outskirts of London in 1770 marked the beginning of the modern circus by providing the essential model that would be refined and expanded as it grew into a global form of entertainment during the nineteenth century. Although many components – equestrian feats, acrobatics, performing animals, rope walking – long antedated Astley’s early displays, it was their combination into a singular show staged within a ring of spectators that gave form to what came to be known as the circus. In this chapter Matthew Wittmann examines the origins of the circus in late eighteenth-century London, contextualising its emergence and tracing its dynamic diffusion across Europe and the Americas during the half century that followed.