The Rohirrim call their land the Mark or the Riddermark, names recalling that of the historical kingdom of Mercia, the region of Western England where Tolkien lived.

Tolkien grounded Rohan in elements inspired by Anglo-Saxon tradition, poetry, and linguistics, specifically in its Mercian dialect, in everything but its use of horses.

It is derived from Elvish *rokkō ‘swift horse for riding’ (Q[uenya] rocco, S[indarin] roch) + a suffix frequent in names of lands [e.g. Beleriand, Ossiriand].

I was aware of this, and liked its shape; but I had also (long before) invented the Elvish horse-word, and saw how Rohan could be accommodated to the linguistic situation as a late Sindarin name of the Mark (previously called Calenarðon 'the (great) green region') after its occupation by horsemen.

The meadows contain "many hidden pools, and broad acres of sedge waving above wet and treacherous bogs"[T 3] that water the grasses.

The cartographer Karen Wynn Fonstad calculated Rohan to be 52,763 square miles (136,656 km2) in area (slightly larger than England).

Rohan is bordered to the north by the Fangorn forest, home to the Ents (tree-giants)[a] led by Treebeard, and by the great river Anduin, called Langflood by the Rohirrim.

[T 4][T 5] To the east are the mouths of the River Entwash, and the Mering Stream, which separated Rohan from the Gondorian province of Anórien, known to the Rohirrim as Sunlending.

To the northwest, just under the southern end of the Misty Mountains, lies the walled circle of Isengard around the ancient tower of Orthanc; at the time of the War of the Ring, it had been taken over by the evil wizard Saruman.

[T 9] In an earlier concept, Rohan's capital region was called the King's Lands, of which the Folde was a sub-region to the south-east of Edoras.

The styles of the Bayeux Tapestry (made in England) fit them well enough, if one remembers that the kind of tennis-nets [the] soldiers seem to have on are only a clumsy conventional sign for chainmail of small rings.

Rohan was bound by the Oath of Éorl to help Gondor in times of peril, and the latter asked for their aid through the giving of the Red Arrow.

This has a historical antecedent in the Old English poem Elene, in which Constantine the Great summoned an army of mounted Visigoths to his aid against the Huns by sending an arrow as a "token of war".

[17] The Rohirrim called their homeland the Riddermark, a modernization by Tolkien of Old English Riddena-mearc, meaning, according to the Index to The Lord of the Rings, "the border country of the knights"; also Éo-marc, the Horse-mark, or simply the Mark.

[20] The Riders' names for the cunningly-built tower of Isengard, Orthanc, and for the Ents, the tree-giants of Fangorn forest, are similarly Old English, both being found in the phrase orþanc enta geweorc, "cunning work of giants" in the poem The Ruin,[21] though Shippey suggests that Tolkien may have chosen to read the phrase also as "Orthanc, the Ent's fortress".

In The Two Towers, chapter 6, the Riders of Rohan are introduced before they are seen, by Aragorn, who chants in the language of the Rohirrim words "in a slow tongue unknown to the Elf and the Dwarf", a lai that Legolas senses "is laden with the sadness of Mortal Men".

To achieve a resonant sense of the lost past, the now-legendary time of a peaceful alliance of the Horse-lords with the realm of Gondor, Tolkien adapted the short Ubi sunt ("Where are they?")

[22][23][24][25]"Thus spoke a forgotten poet long ago in Rohan, recalling how tall and fair was Eorl the Young, who rode down out of the North," Aragorn explains, after singing the Lament.

In the 21st century, a remnant tribe of such Northmen, the Éothéod, moved from the valleys of Anduin to the northwest of Mirkwood, disputing with the Dwarves over the treasure-hoard of Scatha the dragon.

Eorl the Young, lord of the Éothéod, answered the summons, arriving unexpected at a decisive battle on the Field of Celebrant, routing the orc army.

Saruman then launched an invasion of Rohan, with victory in early battles at the Fords of Isen, killing Théoden's son, Théodred.

[T 25] Éomer rode with the armies of Gondor to the Black Gate of Mordor and took part in the Battle of the Morannon against the forces of Sauron.

[T 27] The Tolkien scholar Jane Chance writes that Théoden is transformed by Gandalf into a good bold "Germanic king"; she contrasts this with the failure of "the proud Beorhtnoth" in the Old English poem The Battle of Maldon.

[27] Shippey states further that "the Mark" (or the Riddermark[30]), the land of the Riders of Rohan – all of whom have names in the Mercian dialect of Old English, was once the usual term for central England, and it would have been pronounced and written "marc" rather than the West Saxon "mearc" or the Latinized "Mercia".

Honegger notes that this does not equate the Rohirrim with the Anglo-Saxons (on horseback or not), but it does show a strong connection, making them "the people most dear to Tolkien and all medievalists.

"[11] Jane Ciabattari writes on BBC Culture that Lady Éowyn's fear of being caged rather than "doing great deeds" by riding to battle with the Rohirrim resonated with 1960s feminists, contributing to the success of Lord of the Rings at that time.

For Peter Jackson's The Lord of the Rings film trilogy, the Poolburn Reservoir in Central Otago, New Zealand was used for Rohan scenes.

[34] A fully realised set for Edoras was built on Mount Sunday in the upper reaches of the Rangitata Valley, near Erewhon in New Zealand.