In 4.56 an Athenian fleet is raiding coastal places around the Peloponnese; at the end of the chapter they head for Thyraea, which is currently occupied by the Aeginetans. The narrative continues (4.57):
 προσπλεόντων οὖν ἔτι τῶν Ἀθηναίων οἱ Αἰγινῆται τὸ μὲν ἐπὶ τῇ θαλάσσῃ ὃ ἔτυχον οἰκοδομοῦντες τεῖχος ἐκλείπουσιν, ἐς δὲ τὴν ἄνω πόλιν, ἐν ᾗ ᾤκουν, ἀπεχώρησαν, ἀπέχουσαν σταδίους μάλιστα δέκα τῆς θαλάσσης.  καὶ αὐτοῖς τῶν Λακεδαιμονίων φρουρὰ μία τῶν περὶ τὴν χώραν, ἥπερ καὶ ξυνετείχιζε, ξυνεσελθεῖν μὲν ἐς τὸ τεῖχος οὐκ ἠθέλησαν δεομένων τῶν Αἰγινητῶν, ἀλλ᾽ αὐτοῖς κίνδυνος ἐφαίνετο ἐς τὸ τεῖχος κατακλῄεσθαι: ἀναχωρήσαντες δὲ ἐπὶ τὰ μετέωρα, ὡς οὐκ ἐνόμιζον ἀξιόμαχοι εἶναι, ἡσύχαζον.
The problem with this passage essentially boils down to the meaning of the various instances of τὸ τεῖχος (in bold above). The first clearly refers to the coastal fort which the Aeginetans were building with the help of Lacedaemonian troops from a local garrison. Some commentators take the second and third instances to refer not to the coastal fort, but to the city wall of the upper city (τὴν ἄνω πόλιν). While this is possible, it would seem a bit of a stretch even for Thucydides to use τὸ τεῖχος so confusingly in two different senses so close together. I therefore incline to take all three instances as referring to the coastal fort, and to take ἠθέλησαν as pluperfect in sense. The sequence of events would then be that the Aeginetans retired to the upper city after the Lacedaemonians' refusal to go into the coastal fort with them. On this basis, my translation currently reads:
'While, then, the Athenians were still sailing towards them, the Aeginetans abandoned the coastal fort which they were building at that time, and withdrew to the upper city, in which they lived, and which was about ten stades from the sea. The troops from one of the Lacedaemonian garrisons stationed around the country, who were helping to build the fort, had been unwilling to go into it with the Aeginetans when they asked them to do so, as there seemed to them a danger that they would be penned in there; and after retiring to the heights, as they did not think themselves strong enough to give battle, they remained inactive.'
Does this seem sensible/plausible, or must we accept the use here of τὸ τεῖχος in two senses? Comments would, as always, be much appreciated.