τείχη καθελόντες ἀνθ᾽ ὧν ἡμεῖς τἀκείνων ἐκωλύσαμεν πεσεῖν:
pulling down the walls in return for those that we had prevented from falling.
should the original construction be: αντι τουτων των εκεινων ἅ ἐκωλύσαμεν πεσεῖν , so there is an incorporation of the antecedent here.