Rohan is divided into three areas, or wards, for the purposes of military organization. These are Edoras, the East-mark, and the West-mark. Their boundary is the Snowbourn River to its junction with Entwash, and from there north along the Entwash. The Muster of Edoras is commanded by the First Marshal of the Mark, and it includes Riders drawn from the capital Edoras and adjacent King's Lands (including Harrowdale) and from some parts of the West-mark and East-mark.
The Second and Third Marshals are assigned commands according to the needs of the time. At this time, the ward of the Second Marshal covers areas west of Entwash, including Westfold, Westemnet, Helm's Deep and the Gap of Rohan. The ward of the Third Marshal covers areas east of Entwash, including Eastemnet, Eastfold and the Wold. Each Marshal has at all times one éored stationed at his base of operations to be used as the Marshal sees fit.
Currently, the acting First Marshal is Elfhelm, governing the Riders and other armed men of the garrison of Edoras. The Second Marshal, the King's son Théodred Prince, has command over the West-mark with his base at Helm's Deep; and the Third Marshal, the King's nephew Éomer, has as his ward the East-mark with his base at his home of Aldburg in the Folde. In the Full Muster, the First Marshal commands the leading éored, the King's Company, while the Second and Third Marshals lead the first éoreds of their respective Musters.
Serving under the Marshals are 7 Feldmarshals who act as their advisors and field commanders of whole éoreds in active service during times of peace. Usually, there are two Feldmarshals in the East-mark, two in Edoras, and three in the West-mark. In wartime, the Feldmarshals have such roles that the Marshals decree, but usually they each lead their own companies of several éoreds.
Éoreds have their own commanding officers, known as Æthelwigends ('noble warrior'). The total number of Æthelwigends is approximately 100 in the Full Muster of the Riders, there being perhaps 10 to 20 Æthelwigends in active service during times of peace. However, during peacetime, Æthelwigends rarely command full éoreds, but rather patrols that are detached all over the Mark, watching the borders. Many noble lords usually serve for a time as Æthelwigends in the King's Host, and thus in times of war lead an éored of Riders drawn from their own household and adjacent areas.
Each éored is typically divided into six or more smaller units called patrols, commanded by a patrol leader known as a Mægisterwigend ('master warrior'). The composition of individual éoreds differs between regions, but usually each éored is a self-sustaining unit with its own scouts and supporting personnel such as messengers and healers. If the situation demands it, patrols and éoreds can be combined or split into such groups of Riders that are required for the task at hand. Normally, each patrol consists of 20 Riders (Sperewigends = 'spear warrior'), including the patrol leader.
In the West-mark, it is more common for different patrols within an éored to specialize for a certain role, such as heavy shock troops armed with long spears or fire-support using bows as their main weapon. In the East-mark, such distinctions are usually not made, making the patrols more versatile in different situations than their West-mark counterparts.