The Plague of Justinian (541–542 AD, with recurrences until 750) was a pandemic that afflicted the Byzantine (Eastern Roman) Empire and especially its capital, Constantinople, as well as the Sasanian Empire and port cities around the entire Mediterranean Sea,[1][2] as merchant ships harbored rats that carried fleas infected with plague. Some historians believe the plague of Justinian was one of the deadliest pandemics in history, resulting in the deaths of an estimated 25–50 million people during two centuries of recurrence, a death toll equivalent to 13–26% of the world's population at the time of the first outbreak.[3][4] The plague's social and cultural impact has been compared to that of the Black Death that devastated Eurasia in the fourteenth century,[5] but research published in 2019 argued that the plague's death toll and social effects have been exaggerated.[6][7]