History of the Peloponnesian War

For the island that is called Sphacteria both secures the harbour, by stretching in a line with it, and close off it, and narrows its entrances; on one side, near the Athenian fortifications and Pylus, leaving a passage for two ships; on the other, towards the rest of the mainland, for eight or nine. It was all woody and pathless from its desert condition, and in extent about fifteen stades. The entrances then they intended to bar with a close line of vessels, with their heads looking outwards;

while fearing this island, lest the enemy should carry on their operations against them from it, they conveyed over some heavy-armed troops into it, and posted others along the mainland.