The Antonine Plague was a devastating epidemic that struck the Roman Empire from 165 to 180 AD. It is believed to have been caused by the smallpox virus or possibly measles. The outbreak began during the military campaigns of Emperor Marcus Aurelius and spread rapidly, affecting both soldiers and civilians. The plague resulted in significant population decline, with estimates suggesting that it may have killed up to 5 million people. The social and economic impacts were profound, leading to labor shortages and weakening the Roman Empire's stability. The Antonine Plague is one of the earliest recorded pandemics in history.