It has been suggested that smallpox was a major component of the Plague of Athens that occurred in 430 BCE, during the Peloponnesian Wars, and was described by Thucydides. Galen's description of the Antonine Plague, which swept through the Roman Empire in 165–180 CE, indicates that it was probably caused by smallpox. Returning soldiers brought the disease home with them to Syria and Italy, where it raged for fifteen years and greatly weakened the Roman empire, killing up to one-third of the population in some areas. Total deaths have been estimated at 5 million. A second major outbreak of disease in the Roman Empire, known as the Plague of Cyprian (251–266 CE), was also either smallpox or measles. The Roman empire stopped growing as a consequence on these two plagues, according to historians like Theodore Mommsen. Although some historians believe that many historical epidemics and pandemics were early outbreaks of smallpox, contemporary records are not detailed enough to make a definite diagnosis.