Nicias wished to enable the Athenians to maintain their blockade from this nearer station instead of from Budorum and Salamis; to stop the Peloponnesian triremes and privateers sailing out unobserved from the island, as they had been in the habit of doing; and at the same time prevent anything from coming into Megara.

Accordingly, after taking two towers projecting on the side of Nisaea, by engines from the sea, and clearing the entrance into the channel between the island and the shore, he next proceeded to cut off all communication by building a wall on the mainland at the point where a bridge across a morass enabled succors to be thrown into the island, which was not far off from the continent.

A few days sufficing to accomplish this, he afterwards raised some works in the island also, and leaving a garrison there, departed with his forces.

About the same time in this summer, the Plataean being now without provisions, and unable to support the siege, surrendered to the Peloponnesians in the following manner.