I also managed it in a modest 14 days. Although I reached the Necropolis on day 13, I couldn't defeat it. :( I had to spend a day visiting the Sphinx and the tree.

You're a monster, completing it in 13 days! It's strange that you couldn't defeat the Necropolis. What troops did you have? If you don't recruit the Rakshasa, it just moves forward, but if you do recruit it, it practically stays in place.
Well, if you visited the Sphinx, then you must have gained a lot of experience. What level were you before the final battle??? I was level 20, and they gave me another level after the battle.

I knew there would be very close results. :)