I've been wondering this for awhile now. Where exactly is Akavir? I've never seen it on any map I've come across or heard/read where it is located. Oh, and one other thing. Cyrodiil went to war with Akavir, correct? Then why do the blades use katanas, the weapons of their former foes, instead of emperial made weapons?

Akavir is east of Tamriel.

At one point in history, Akaviri warriors were assimilated into Imperial Culture(so deeply that one Tamrielic emperor was Akaviri), so the Imperials(specifically Nibeneans) still retain some Akaviri culture, specifically in military design.

I always thought it was South of Tamriel. Just curious, but in what era were the Akavir in Tamriel?

The Akaviri first invaded Tamriel during the first era, but they were in power as emperors in the second era. Eventually, in the third era, Tamrielic soldiers invaded Akavir(http://www.uesp.net/wiki/Lore:Report:_Disaster_at_Ionith).

Here is a map that shows Tamriel. http://i35.tinypic.com/2r6my3d.jpg

The continents of Atmora and Akavir only shown in direction though.

The Akavir influence as mentioned by seti, was specifically from the Tsaesci. The Akavir "rule" followed the assassination of Reman and began the 2nd era.