Aha, this might be a deliberate part of a puzzle. (Sorry, it's been a while since I wrote the game, so I couldn't remember it myself!)
*** SPOILERS FOLLOW *** - to decode rot13, see https://rot13.com
If you lead Achilles into the fort under circumstances — [rot13: jura uvf obbgf ner bss naq uvf Npuvyyrf' urryf ner ihyarenoyr] — you won't be able to leave until Hector kills him. When you try, you ought to see a message like ""Achilles dodges a swing and jumps in front of you, blocking your way out." Is it possible you were missing that message?
If you want Achilles to win, you'll need to solve the puzzle a different way.