Thucydides, History of the Peloponnesian War
Benjamin Jowett, Ed.

69. The Athenian generals became aware that some difficulty had arisen, and that they could¹ not carry the city by storm. So they² immediately set about the circumvallation of Nisaea, thinking that, if they could take it before any assistance arrived, Megara itself would be more likely to capitulate. [2] Iron and other things needful, as well as masons, were quickly procured from Athens. Beginning from the wall which they already held they intercepted the approach from Megara by a cross wall, and from that drew another on either side of Nisaea down to the sea. The army divided among them the execution of the trench and walls, obtaining stones and bricks from the suburbs of the town. They also cut down timber and fruit-trees and made palisades where they were needed. The houses in the suburbs were of themselves a sufficient fortification, and only required battlements. [3] All that day they continued working; on the following day, towards evening, the wall was nearly finished, and the terrified inhabitants of Nisaea having no food (for they depended for their daily supplies on the upper city), and imagining that Megara had gone over to the enemy, despairing too of any aid soon arriving from Peloponnesus, capitulated to the Athenians. The conditions were as follows:— They were to go free, every man paying a fixed ransom and giving up his arms; but the Athenians might deal as they pleased with the Lacedaemonian commander and any Lacedaemonian who was in the place. [4] Upon these terms they came out, and the Athenians, having broken down the Long Walls between Megara and Nisaea, took possession of Nisaea and prepared for further action.