E.C. Marchant, Commentary on Thucydides Book 1

[3] 17. τὴν μὲν γὰρ κτλ.—this is taken in two ways: (1) τὴν μέν object of παρασκευάσασθαι and πόλιν ἀντίπαλον in apposition= ὥστε γενέσθαι πόλιν ἀντίπαλον (Krüger etc.); (2) τὴν μέν accus. of respect, ‘as regards the one’ (Shilleto, Classen, etc.). The sense is clearly given by Arnold: ‘Pericles is distinguishing between two different methods of ἐπιτείχισις, the one by founding a city in the neighbourhood of Athens strong enough to interfere with her trade and be a check on her power, πόλιν ἀντίπαλον: the other by merely raising one or two forts in Attica, as strongholds for plundering parties to keep the country in constant annoyance and alarm, φρούριον.’ The only difficulty is that ἐπιτείχισις is nowhere found of a rival city founded in time of peace; hence (2) is probably the constn. intended.

18. ἦ που δή—of course, then, sc χαλεπόν ἐστι.

19. ἐκείνοις ἡμῶν ἀντεπιτετειχισμένων—this seems to refer to the certainty that Athens would reply to an ἐπιτείχισις by taking similar measures in Peloponnesian territory (Pylus, Cythera): hence we look for a future; and ἀντεπιτειχιουμένων, ἀντεπιτετειχισομένων or the insertion of ἄν has been proposed. Another view is that Athens herself is meant; she is already standing as an ἐπιτείχισις threatening any post that Sparta might establish in Attica. Since an ἐπιτείχισις always occurs in an enemy's country, this could only be justified by supposing that Pericles uses the term loosely for the sake of the antithesis. But it certainly looks as if something to be done by Athens is meant.