Introduction:
Rohan was a great kingdom of Men, located in the land once known as Calenardhon, situated in the great vale between the Misty Mountains to the north and the White Mountains to the south. The land of Rohan extended from the fords of the river Isen in the west, up to the shores of the river Anduin in the east. The forest of Fangorn lay within the borders of Rohan, and the Elven city of Lorien lay to the north of the river Limlight.
The land of Rohan was originally part of Gondor, but gained independence from it. The land was first known as “Rohan” to the Men of Gondor, and its people the Rohirrim, meaning ‘the Horse-lords’, but the people of Rohan called themselves the Eorlingas, sons of Eorl the Young, first King of Rohan, as the land of Calenardhon was given in gift to Eorl and his people by Cirion, Steward of Gondor, in thanks for their service to Gondor in battle against the Balchoth. Eorl, the first king, swore an oath of friendship, at need or at call, to the Lords of Gondor, and thus the Rohirrim became the greatest allies of the Men of Gondor throughout the Third Age and beyond. They were known for their cavalry and horse training, which came into use countless times in battles such as the Battle of the Hornburg and on the Pelennor Fields.
History:
Descent from the Northmen:
In the 1200s of the Third Age, the Kings of Gondor made alliances with the Northmen of Rhovanion, a people thought to be distantly descended from the Edain, those peoples of Men who crossed into Beleriand in the First Age and later settled in Númenor. The men who would become the Rohirrim were in fact more closely akin to the Beornings and the Men of Dale, and are accounted as Middle Men, who, while not directly descended from the Men of Númenor, never served the will of Sauron. In “The Two Towers”, Aragorn describes the Rohirrim thusly:
“They are proud and wilful, but they are true-hearted, generous in thought and in deed; bold but not cruel; wise but unlearned, writing no books but singing many songs, after the manner of the children of Men before the Dark Years […]. It was in forgotten years long ago that Eorl the Young brought them out of the North, and their kinship is rather with the Bardings of Dale, and with the Beornings of the Wood, among whom may still be seen many men tall and fair, as are the Riders of Rohan.”
In the early part of the Third Age, such men occupied a territory known as Rhovanion, the lands east of Mirkwood, Greenwood the Great, west of the inland Sea of Rhûn, and south of the Celduin (the River Running). While never united under one singular king, the Men of Rhovanion nonetheless were allies of Gondor, and many of the great Princes of Rhovanion and their kin served in the armies of Gondor. In this way was the ruling House of Gondor mingled with the Northmen during the reign of King Eldacar, and the Northmen intermarried with the Dúnedain of the South and were eventually reckoned Men of Gondor. Through nearly constant conflict with the Men of Rhûn (Balchoth, Wainriders, and the like), the population of Rhovanion dwindled.