For hundreds of years in the Mythic Era, raiders crossed the Sea of Ghosts to invade Tamriel from the frozen lands of Atmora, becoming after generations of living in our land the Nords, Imperials, and the Bretons of today. The last invasion occured in 1E 68 with the two ships being mostly laden with corpses. The description of the land these raiders left changes radically over the years, leaving many to beleive that it was gradually dying, smothered by frost. Expeditions to Atmora in the Third Era describe a place of permanent winter, with little life and no signs of human habitation.
Even before the frost fall, Atmora was apparently not a temperate place. The early Nedic peoples who came from Atmora were hunters with no knowledge of agriculture. A land where every denizen was a predator doubtlessly insured that only the most brutal and savage survived. It is easy to see how these traits passed the raider men and down to the nature of the Arena of Tamriel. [source?]