User blog comment:Darkcloud1111/''The Mark of Athena'' Plot Holes/@comment-3146930-20121011002344/@comment-173.79.138.71-20121013174334

Hyperborean posted this: Otis and I [Ephialtes] have been imprisoned under Rome for eons, but we’ve kept busy building our very own hypogeum.

I would like to point out that they may have been helping out Arachne for centuries and been building their hypogeum while they were in Tartarus. After all, the floor under Arachne did lead to Tartarus, so they may have been directing monsters above.