While the Spartans' siege preparations were underway, the Athenian fleet, 50 triremes strong, arrived from Zacynthus. The Spartans failed to blockade the entrance of the harbour, so the Athenians were able to sail in and catch the Spartans unprepared; the Spartan fleet was decisively defeated, and the Athenians gained control of the harbour. In doing so, they trapped 420 Spartan hoplites on the island of Sphacteria, off Pylos. 120 of these were from the Spartiate class, and their peril threw the Spartan government into a panic. Members of the government were dispatched to the scene, and negotiated an armistice on the spot; the entire Spartan fleet was surrendered to the Athenians as a guarantee for Spartan good conduct, and ambassadors were sent to Athens to seek a permanent peace. When these negotiations failed, the Athenians retained possession of the Spartan ships on a pretext, and settled in to besiege the hoplites on Sphacteria; eventually, in the Battle of Sphacteria, those hoplites were captured and taken as hostages to Athens. Pylos remained in Athenian hands, and was used as a base for raids into Spartan territory and as a refuge for fleeing Spartan Helots.