Riddle me this

So A Sphinx(in one version, thanks Wikipedia ) guards the entrance to the Greek city of Thebes, but I wanted It to guard the entrance to a more mysterious place, somewhere inside the ruins of a Egyptian like tomb.
In It's hand the Sphinx holds a scroll with of It's legendary riddles
"There are two sisters: one gives birth to the other and she, in turn, gives birth to the first."
So I translated the riddle into Greek and that is what you see on the scroll.

I am pleased with this piece, but definitely could put a lot more details in to it and work on the highlights