E.C. Marchant, Commentary on Thucydides: Book 3

διὰ κατάγνωσιν ἀσθενείας σφῶν=διὰ τὸ καταγνῶναι σφῶν ἀσθένειαν, i.e. σφῶν depends on κατάγνωσιν. On what the ‘imputation’ was based can be seen from c. 13.

τὸ ἐπὶ Λέσβῳ ναυτικόν—the suggestion of the speaker in c. 13 was απ᾽ αμφοτέρων (Lesbos and Peloponnese) ἀποχωρήσονται: but what is mentioned in c. 7, 3 had meantime occurred.

αὐτοί—these, as the restriction shows, consisted of the ζευγῖται and θῆτες. The two higher classes served on board only in times of great danger.

παρὰ τὸν Ἰσθμὸν ἐπίδειξιν ἐποιοῦντο ‘made a demonstration along the coast of.’ With ἀναγαγόντες instead of the ordinary ἀναγαγόμενοι cf. Herod. VI. 12 ἀνάγων τὰς νέας.

ἀποβάσεις—the plan of making descents on the enemy's coasts as a counter-move to the invasion of Attica had been started by Pericles.