Courtesy of our friends as TIL:
Reman
Culture god-hero of the Second Empire, Reman was the greatest hero of the Akaviri Trouble. Indeed, he convinced the invaders to help him build his own empire, and conquered all of Tamriel except for Morrowind. He instituted the rites of becoming Emperor, which included the creation of the Amulet of Kings, a soulgem of immense power. His Dynasty was ended by the Dunmeri Morag Tong at the end of the first era. Also called the Worldly God
Culture god-hero of the Second Empire, Reman was the greatest hero of the Akaviri Trouble. Indeed, he convinced the invaders to help him build his own empire, and conquered all of Tamriel except for Morrowind. He instituted the rites of becoming Emperor, which included the creation of the Amulet of Kings, a soulgem of immense power. His Dynasty was ended by the Dunmeri Morag Tong at the end of the first era. Also called the Worldly God
That includes the Summurset Isles, a nation so thick with master wizards that Tiber "D.B." Septim needed a dragon-[censored] brass gundam to subdue.
So how could he have possibly taken it? Did he just flood them with so many legionnaires that there simply wasn't enough room to cast a spell? Imperial Battlemages? Or perhaps the Altmer just scared of all the http://www.motifake.com/image/demotivational-poster/0712/katana-martial-arts-demotivational-poster-1196895838.jpg that the Tsaesci had?