Sparta was dependent on the helots, who tended the fields while its citizens trained to become soldiers. The helots made the Spartan system possible, but now the post off Pylos began attracting helot runaways. In addition, the fear of a general revolt of helots emboldened by the nearby Athenian presence drove the Spartans to action which culminated with the Athenian naval victory at the Battle of Pylos. An Athenian fleet had been driven ashore at Pylos by a storm, and, at the instigation of Demosthenes, the Athenian soldiers fortified the peninsula, and a small force was left there when the fleet departed again. The establishment of an Athenian garrison in Spartan territory frightened the Spartan leadership, and the Spartan army, which had been ravaging Attica under the command of Agis, ended their expedition (the expedition only lasted 15 days) and marched home, while the Spartan fleet at Corcyra sailed to Pylos.