Two of the most powerful city-states in ancient Greece—Sparta and Athens—went to war in 431 B.C. Tensions between the two had been simmering for decades before boiling over into war. Occupying the lands of the Peloponnese (mainland Greece’s southern-most peninsula), Sparta enacted a land-based strategy, relying on their disciplined hoplites to defeat the Athenians in the open field. When Spartan troops would invade Attica (the peninsula where Athens and its allies were located), Athenians responded with naval attacks on politically sensitive points in the Peloponnese. Rural populations in Attica would be forced to take refuge within Athens’s city walls when Sparta invaded.
The Peloponnesian War would end by fundamentally shifting power in the Mediterranean, but neither Athens’s navy nor Sparta’s soldiers could claim to be the determining factor of the conflict. That honor belongs to an event that nobody could have predicted or planned for: the plague of Athens, which broke out in the war’s second year. A medical mystery to this day, this ancient epidemic would be the most influential factor to shape the war and decide which city-state would be the final victor.
In spring 430 B.C. locals in Piraeus, the port area of Athens, began to fall ill with a disease no one had seen before. The malady spread quickly. Reports circulated of similar outbreaks on the island of Lemnos, in the north Aegean, and other locations.
