User blog comment:Darkcloud1111/''The Mark of Athena'' Plot Holes/@comment-3146930-20121014230006/@comment-5112532-20121016184752

Maybe the Doors of Death moved to Tartarus, due to Gaea's power? And he can't get in? It is said, that Thantos cannot close them himself, maybe because he can't go in to that pit.

I dunno... :L