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, towards the close of this summer, Rhamphias, Autocharidas, and Epicydidas, who were Lacedaemonians, were on their way with reinforcements, consisting of nine hundred hoplites, to the strongholds in Thrace, and arriving at Heracleia in Trachis they set in order whatever seemed to them amiss.
It was while they were staying there that the battle at Amphipolis occurred; and so the summer ended.