The epidemic there killed the 13-year-old son of the Byzantine emperor, John VI Kantakouzenos, who wrote a description of the disease modelled on Thucydides's account of the 5th century BCE Plague of Athens, but noting the spread of the Black Death by ship between maritime cities. Nicephorus Gregoras also described in writing to Demetrios Kydones the rising death toll, the futility of medicine, and the panic of the citizens. The first outbreak in Constantinople lasted a year, but the disease recurred ten times before 1400.