According to the above statement Athens had in 431 a field force of 13,000 and a garrison force of 16,000 ‘oldest and youngest and aliens,’ both apparently consisting solely of hoplites. Let us examine the different categories composing the garrison force. A roll was kept of all Athenians between the ages of 18 and 60, and these men were all liable to some sort of service (Arist. Resp. Ath. 53, Pollux 2. 11). For the first two years of their service the young Athenians were enrolled among the περίπολοι and after a preliminary training they were sent to guard the frontier forts (φρουροῦσιτὰ δύο ἔτη Arist. Resp. Ath. 42). The words ἐν τοῖς φρουρίους in the passage before us, leave little doubt that these are the men designated as νεώτατοι On the same principle we are entitled to look for the πρεσβύτατοι among the oldest men included on the roll, not among the citizens over 60 years of age. The normal age at which an Athenian was transferred from the field force to the reserve was apparently 50: thus Lycurgus (in Leocr. 39) speaks of Athens being defended by men over 50 after the battle of Chaeronea, and Socrates, who served at Amphipolis when in his forty-seventh year (Plato, Apol. 28 E), is not heard of on foreign expeditions after that date, though Plato was fond of referring to his exploits on active service (Symp. 219 E, Charm. 153 A, Laches 181 A).