n its most famous attestation, in Classical Athens, the office of strategos existed already in the 6th century BC, but it was only with the reforms of Cleisthenes in 501 BC that it assumed its "classical" form: a board of ten strategoi who were elected annually, one from each tribe (phyle). The ten were of equal status, and replaced the polemarchos, who had hitherto been the senior military commander. At Marathon in 490 BC (according to Herodotus) they decided strategy by majority vote, and each held the presidency in daily rotation. At this date the polemarchos had a casting vote, and one view is that he was the commander-in-chief; but from 486 onwards the polemarchos, like the other archontes, was appointed by lot. The annual election of the strategoi was held in the spring, and their term of office coincided with the ordinary Athenian year, from midsummer to midsummer. If a strategos died or was dismissed from office, a by-election might be held to replace him.

The strict adherence to the principle of a strategos from each tribe lasted until ca. 440 BC, after which two strategoi could be selected from the same tribe and another tribe be left without its own strategos, perhaps because no suitable candidate might be available. This system continued at least until ca. 356/7 BC, but by the time Aristotle wrote his Constitution of the Athenians in ca. 330 BC, the appointments were made without any reference to tribal affiliation. Hence, during the Hellenistic period, although the number of the tribes was increased, the number of strategoi remained constant at ten.

In the early part of the 5th century, several strategoi combined their military office with a political role, e.g. Themistocles, Aristides, Cimon, or Pericles; nevertheless their power derived not from their office, but from their own personal political charisma. As political power passed to the rhetores in the later 5th century, the strategoi were limited to their military duties. Originally, the strategoi were appointed ad hoc to various assignments. On campaign, several—usually up to three—strategoi might be placed jointly in command, and, unlike other Greek states where the office of nauarchos commanded the navy, the Athenian strategoi held command both at sea and on land. From the middle of the 4th century, the strategoi increasingly were given specific assignments, such as the strategos epi ten choran for the defence of Attica; the strategos epi tous hoplitas, in charge of expeditions abroad; the two strategoi epi ton Peiraia, responsible for the war harbour of Piraeus; and the strategos epi tas symmorias, responsible for the equipment of the warships. This was generalized in Hellenistic times, when each strategos was given specific duties. One of them, the strategos epi ta hopla, ascended to major prominence in the Roman period.

The Athenian people kept a close eye on their strategoi. Like other magistrates, at the end of their term of office they were subject to euthyna and in addition there was a vote in the ekklesia during every prytany on the question whether they were performing their duties well. If the vote went against anyone, he was deposed and as a rule tried by jury. Pericles himself in 430 was removed from office as strategos and fined, and in 406 the eight strategoi who commanded the fleet at the Battle of Arginusae were all removed from office and condemned to death.

The title of strategos appears for a number of other Greek states in the Classical period, but it is often unclear whether this refers to an actual office, or is used as a generic term for military commander. The strategos as an office is attested at least for Syracuse from the late 5th century BC, Erythrae, and in the koinon of the Arcadians in the 360s BC.

The title of strategos autokrator was also used for generals with broad powers, but the extent and nature of these powers was granted on an ad hoc basis. Thus Philip II of Macedon was elected as strategos autokrator (commander-in-chief with full powers) of the League of Corinth.