Board Thread:Lore Discussion/@comment-202.28.118.123-20150414075356/@comment-6881629-20150414090228

That happened between Oblivion and Skyrim, Oblivion ends about 4E 1 the Thalmor present the Emperor with the Blades heads in 4E 171 then Skyrim starts at 4E 201. The very long timeline page is here.