A regiment in the Kingdom of Valyria, also called a column, is the total body of troops committed by a single duke from his duchy for muster. Dukes usually lead regiments as colonels, and a colonel is the rank given to a leader of a regiment, but dukes sometimes appoint others to lead the forces from their duchies. The deputy or second in command of a regiment is called a constable, and constables are often a fixture of ducal cabinets.
The term regiment implies a set of regulations and governance “regimented” by the captain of a group of captains, aka the colonel, and embodied in written contracts. Thus, the “regiment” are all the captains who have subscribed under the fealty of the duke, who is the colonel or column leader.