The city of Mytilene attempted to unify the island of Lesbos under its control and revolt from the Athenian Empire. In 428 BCE, the Mytilenean government planned a rebellion in concert with Sparta, Boeotia, and certain other cities on the island, and began preparing to revolt by fortifying the city and laying in supplies for a prolonged war. These preparations were interrupted by the Athenian fleet, which had been notified of the plot. The Athenian fleet blockaded Mytilene by sea. On Lesbos, meanwhile, the arrival of 1,000 Athenian hoplites allowed Athens to complete the investment of Mytilene by walling it in on land. Although Sparta finally dispatched a fleet in the summer of 427 BCE, it advanced with such caution and so many delays that it arrived in the vicinity of Lesbos only in time to receive news of Mytilene's surrender.