History of the Peloponnesian War
Thucydides
Thucydides. The Peloponnesian War. London, J. M. Dent; New York, E. P. Dutton. 1910.
The Athenian envoys now returned to the army; and the Melians showing no signs of yielding, the generals at once betook themselves to hostilities, and drew a line of circumvallation round the Melians, dividing the work among the different states.
Subsequently the Athenians returned with most of their army, leaving behind them a certain number of their own citizens and of the allies to keep guard by land and sea.
The force thus left stayed on and besieged the place.