The episode in the bastion does little to advance the plot, but it does emphasize the daring and inventive bravado of the musketeers and d'Artagnan. Of course, the purpose of their going to the bastion, apart from its being a daring excursion, is to find a place where they can discuss secret strategy without being overheard. We know that the cardinal has spies in every nook and cranny of France — if not in all of Europe — therefore, only in a captured and temporarily abandoned bastion can they find sufficient privacy to make plans to thwart Milady's scheme to kill Constance Bonacieux and d'Artagnan.
Athos is characterized in this episode as a true leader: he knows that the muskets belonging to the dead soldiers are still beside their bodies, and by placing the dead men and their muskets on the bastion's parapet, he shows great ingenuity: the attacking soldiers will be firing at dead bodies while the musketeers will be taking direct aim at the attacking soldiers.
Once again, during their discussion about Milady, we realize that she is one of the most villainous and crafty women imaginable. She is totally amoral; she will sacrifice anyone to her deadly, vengeful schemes.
It is interesting to see how several earlier adventures prepared the way for these present adventures. For example, if Planchet had not accompanied d'Artagnan on the trip to England, he would not know how to get there now. Likewise, because Bazin is known by Madame de Chevreuse as Aramis's servant, he will be recognized and trusted.
