Orsinium is the ancestral homeland of the Orsimer, a fortification looking city built upon the Whrotgarian mountains between High Rock and Skyrim. Historically, this city was destroyed and rebuilt multiple times, a symbol of the Orsimer’s fate to be homeless but a testament to their resillience. The last time to be rebuilt was during the Third Era, with the support of the Empire. The city managed to continue to exist throughout the Fourth Era, although many Orsimer had left the city to return to life in orc camps. However, late in the Fourth Era, Orsinium managed to land a good investment deal with the Empire.
The Bond of New Orsinium was signed between the Empire and Orsinium, renaming the city to New Orsinium. This agreement provided New Orsinium with a steady flow on gold to aid its expansion, and in return, the Orsimer were to provide strong warriors to help the Empire when in need. This military aid has yet to be called upon, but the Orsimer are always ready to go to battle.
