The beginning of the Peloponnesian War was marked by a violent epidemic that ravaged the population of Attica. The exact nature of the disease is unknown.
Bouchard, Elsa. "Plague of Athens". The Literary Encyclopedia. First published 01 March 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=11226, accessed 02 September 2014.]