The earliest recorded pandemic happened during the Peloponnesian War. It passed through Libya, Ethiopia, and Egypt, and it reached Athens as the Spartans laid siege. Two-thirds of the population died. The disease, suspected to have been typhoid fever, weakened the Athenians significantly and played a big role in their defeat by the Spartans.
It may have been an early appearance of smallpox that began with the Huns. The Huns then infected the Germans, who passed it to the Romans and then returning troops spread it throughout the Roman empire. This plague continued until about 180 A.D., claiming Emperor Marcus Aurelius as one of its victims.
Epidemic is a term that is often broadly used to describe any problem that has grown out of control. An epidemic is defined as "an outbreak of a disease that occurs over a wide geographic area and affects an exceptionally high proportion of the population." An epidemic is an event in which a disease is actively spreading.