Rohan was a Mannish kingdom on the northern borders of Gondor. It was the territory of the Rohirrim, a people of herdsmen and farmers. Well-known for their horses and cavalry, they were Gondor's most important ally.

The borders of Rohan were the river Isen from its junction with the river Adorn and then northwards to the outer walls of Isengard and the river Adorn in the west; from the outer walls of Isengard eastwards and northwards along the eaves of Fangorn Forest to the river Limlight in the north; the river Anduin and the west-cliff of the Emyn Muil hills down to the marshes of the mouths of the river Entwash and beyond those marshes the Mering stream that flowed from the Wood of Anwar to join the river Entwash in the east and the White Mountains as far as the end of their northward arm in the south.. The most significant feature of Rohan's geography was the river Entwash, which divided the country between Eastemnet and Westemnet, itself divided as Eastfold and Westfold. Other lands were the Wold, the Folde, the line of downs to the north-west of the East Wall of Rohan and the Undeeps. Ted Nasmith - The Riders of Rohan The Rohirrim found abandoned Gondorian fortresses and refuges in the White Mountains, such as Dunharrow, Orthanc and the Hornburg which they restored and used themselves. The capital of Rohan was the hill fort of Edoras which lay on the slopes of the White Mountains. Another large city was Aldburg, the capital city of the Eastfold and original city of Eorl the Young. Other cities must have existed but are not named. At the time of the War of the Ring, Rohan was roughly a third the size of Gondor, whose borders had slowly been shrinking for decades.