History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
About the same time the Lacedaemonians, too, marched out with all their forces to Leuctra, a place on their own borders opposite Mt. Lycaeum, under the command of King Agis son of Archidamus; and no one knew whither they were marching, not even the cities from which they were sent.