The Plague of Justinian was a pandemic caused by bubonic plague. It happened during the years of 541 to 542 in the Byzantine Empire. It was the first pandemic recorded in history. Historians estimate that this pandemic killed as many as 100 million people across the world, partly because it returned every twelve years until 770, when it stopped for about 500 years.
Between 541 and 700, the Plague of Justinian killed about half of the people in Europe. It also may have contributed to the success of the Muslim conquests. Its social and cultural impact is comparable to that of the Black Death.