User blog comment:Darkcloud1111/''The Mark of Athena'' Plot Holes/@comment-3146930-20121014230006/@comment-3146930-20121023201901

The "Multiple Doors of Death" idea is the only idea I can think of that makes the Doors of Death not a plot hole. If Gaea isn't able to actually capture them because it is Thanatos' symbol of power like you are suggesting, then why would Thanatos make a door in Tartarus for any reason? I mean you could say he was tricked into making the door, but what reason would he have for making a door to Tartarus. If the Doors of Death is always in Tartarus, then Thanatos would never use them as not even the gods go to Tartarus.

As far as the doors being his Symbol of Power, I don't think they are as he just uses them as passage in and out of the Underworld. I think this because it has been said that Gaea forced the doors open, Thanatos admitting that he was not strong enough to close them as Gaea was more powerful, and Nico stating that the only reason Hades hadn't closed the doors was because they were in Tartarus. From this, it sounds like anyone can use the doors, but Thanatos is the only one that really uses them as he is the one that polices the borders of the dead and the living.