The account given by Thucydides (I. 107. 2–108. 2) of the Spartan expedition to Central Greece that culminated in the battle of Tanagra is not entirely satisfactory. The main problem that arises out of it may be put in the form of a question: why did the Spartans need such a large force, namely 1,500 hoplites ‘ἑαυτῶν’ with 10,000 more ‘ τῶν συμμάχων ’, merely for the purpose of coercing the Phocians? It is not, I think, an unreasonable criticism to say that the aim and strength of the expedition, as given by Thucydides, seem quite out of proportion, and most modern historians have found it difficult to accept his account in full. The problem has usually been solved by assuming that the Spartans had an ulterior motive, namely the re-establishment of a strong Thebes as a check to Athens. But a careful reading of Thucydides should make it quite clear that he at any rate knew nothing of any ulterior motive. For at the beginning of his account he gives the Spartans' desire to protect the people of Doris as the sole motive for the expedition. Then, he goes on, after dealing with the Phocians the Spartans started out on the homeward journey (‘ άττεχώρουν πάλιν ’). But finding that they were cut off by the arrival of an Athenian squadron in the gulf of Corinth, while the land route was already blocked because of the Athenians' control of the Megarid, ‘ they decided to remain in Boeotia and consider what was the safest way for them to get home ’. The Athenians thereupon marched into Boeotian territory to oppose them, and the result was the battle at Tanagra. This account, I think, makes it sufficiently plain that in Thucydides' opinion the battle of Tanagra was entirely the result of an Athenian attempt to trap the Spartan expeditionary force, and that if left to themselves the Spartans would have gone straight home after dealing with the Phocians. Thus the usual answer to the problem involves a serious departure from Thucydides' account of the affair. But in addition this theory of an ulterior move directed by Sparta against Athens does not fit in at all well with what is known of Spartan policy during this period. For it is remarkable that throughout the fifteen years of the First Peloponnesian War Spartan activity against Athens was almost nil, in spite of many attacks on members of her confederacy, the complete subjugation of at least one of them, Aegina, and several raids oh her own territory: apart from the Tanagra campaign, the only positive action taken by the Spartans themselves was the rather half-hearted invasion of Attica led by Pleistoanax in 446. It is beyond the scope of this note to consider the reasons for this inactivity on the part of Sparta, but the fact that they were so little active at this time gives very good grounds for believing Thucydides' account of the original cause of the campaign under consideration.