This article presents a case of osteomyelitis variolosa from a skeleton excavated in the Western Cemetery at Cirencester (Corinium) in Britain, dated to the 3rd or 4th c. CE. This osteological condition is caused by the variola virus, the causative agent of smallpox, and is found in some individuals who have survived a childhood smallpox infection, the condition manifesting many years later. The significance of this discovery is that it indicates that smallpox had been introduced into the Roman world, and to Britain in particular, by the late 3rd or 4th c. CE. Rather than postulating a separate and unrecorded introduction of smallpox into the Roman empire, we suggest that this discovery strengthens the case for seeing the 2nd-c. Antonine Plague as an early form of smallpox.