Tsaesci

East of Tamriel lies the land of the dragons, known as the continent of Akavir. There is very little known about the continent. Many times have Akaviri forces tried to invade Tamriel, but they have always been fended off by the forces of Tamriel. In the "Pocket Guide to the Empire, 3rd Edition" there is a segment about the Battle of Pale Pass, which was fought between the Akaviri race known as Tsaesci, and the Cyrodiilic Emperor Reman the First. After defeating the Tsaesci, Reman made some of the prisoners his advisers to help give insight to the strange continent of Akavir. The little information known about the races and culture of Akavir comes from this period.

Pale Pass is located in Skyrim and Reman was the emperor of Cyrodiil, which means that the Tsaesci invaders must have arrived from either Morrowind or the northern part of Skyrim before beginning their assault. 

Judging by the map, the Tsaesci navy could have landed near the present city of Winter Hold. They could also have moved through Morrowind, but then the army would probably have gone south, not through the mountain chain between Morrowind and Skyrim, simply to move through a new mountain chain to get to Cyrodiil from Skyrim.

The Tsaesci is a snake-like people. If they could they would have avoided going through cold landscapes. Maybe it is the reason why they lost the Battle of Pale Pass, because they were not prepared for the cold landscapes of Skyrim. Another thing is confusing about the invasion. In the "Report: Disaster at Ionith", which was written during the attempt to colonize Akavir in 3E 288, the writer says that the Akaviri inhabitants didn't seem to have any navy to speak of. If the Tsaesci had no navy after a thousand years, how did they get to Tamriel in the first place? Where they so desperate that a whole army swam across the sea? Are the Tsaesci running from something back home, if so it could be the reason why the Akaviri inhabitants have tried to invade Tamriel so many times.

After Reman the Third was assassinated by Morag Tong in 1E 2920, a Tsaesci known as Versidue-Shaie took over the throne and started the Second Era. He Ruled in over 300 years before too being assassinated. That means that a Tsaesci have been in charge of Cyrodiil, yet there is hardly anything known about the race Tsaesci.

 /R

(Note from the 25 of July: I have recently found evidence that they actually moved through Morrowind. For more information see 108 days left - The Battle of Pale Pass, What Really Happened)