Who mutilated the herms?
On the morning of June 7, 415 B.C., the people of Athens woke up to discover that all the statues of Hermes, called herms, had been obscenely disfigured.
Since Hermes was the god of travelers, the message was clear: The planned military expedition against Syracuse, scheduled to depart that very afternoon, should be called off.
For political reasons, the finger was pointed at the general in charge, Alcibiades, who was probably innocent.
The expedition sailed anyway, but Alcibiades knew that when he got back he'd be tried for treason, win or lose. So he defected to the enemy at the first opportunity, with fatal results for the expedition.
It was the turning point in the Peloponnesian War, which ended in Athens' utter defeat.