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

κατὰ τὸν χρόνον τοῦτον ὅν—i.e. καθ᾽ ὄν, according to a common idiom; cf. Soph. OC. 748 ἐς τοσοῦτον αίκίας πεσεῖν | ἔδοξ᾽, ὅσον πέπτωκεν ἥδε.

ἐν τοῖς πλεῖσται δή—for the fem. cf. c. 82, 1 (στάσις) ἐν τοῖς πρώτη ἐγένετο. Pre-eminence is not necessarily implied in any of the examples of this idiom, and Herbst is perhaps right in saying that prominence only is meant. The latter must be the point here, because of παραπλήσιαι δὲ καὶ ἔτι πλείους.

δή heightening the superlative is not elsewhere added to this idiom.

αὐτοῖς—with ἐγένοντο.

ἐνεργοὶ †κάλλει makes no sense. ἐνεργός, though not elsewhere applied to ships, is well suited to them, ‘on active service,’ ‘in commission’; and it may be that the note in Hesychius αἱ μὴ ἀργαί alludes to this passage. But κάλλει must be corrupt, for the rendering ‘effective by their fine condition’ is not possible. Herbst's conjecture ς´ καὶ λ́, i.e. 230, is plausible; but in order to make up so great a total, he assumes a fleet of sixty ships for guarding the eoast of Attica. Were this so, we should surely have heard of it at c. 16, 2 among the reasons that caused the Pel. to abandon the invasion; and even though we are left to collect the number of ships at sea in 428 B.C., this large item in the total must have been mentioned somewhere. Still, the interpolator may have reckoned the total at 230 by the same proeess, whatever it was, that led him to 250 for 431 B.C. below. The number, however, does not come in naturally after ἐν τοῖς πλεῖσται. A very good sense would be got by μιᾷ πόλει (Widmann).