Board Thread:Lore Discussion/@comment-10561605-20130820164006/@comment-6881629-20150713150330

Alessia kind of is the Amulet of Kings it's a soul gem containing her soul and her sucsesor Belharza may have been her son.

Back on topic though i think the first comment was correct no one could get to wall inside Sky Haven as it was sealed with a lock requiring the blood of a Dragonborn to open, and after construction may have been pretty much left alone. It may even of been made just for the Last Dragonborn to show the truth of what was actually going on when the time came for the final part of the prophesy. There was one person who worked it all out though even without the wall, Esbern but no one believed him.