Rohan is the territory of the Rohirrim, a people of herdsmen and some farmers on the northern borders of Gondor in Middle-earth.
Conceptualized as the "Horse kings of Rohan" allied with Mordor in early drafts of 1939, the Rohirrim took their final form in 1942 when the text of the Lord of the Rings was completed to about one third.
Rohan has gone through great lengths to fulfil their part of the treaty including sacrificing two of its heirs when Gondor was under threat from the Haradrim in 2885, when Fastred and Folcred, the twin sons of KingFolcwine, were killed during the Battle of Crossings of Poros.