Master of the Horse is an official position in several European nations. It was more common when most countries in Europe were monarchies, and is of varying prominence today.
(Ancient Rome)
The original Master of the Horse () in the Roman Republic was an office appointed and dismissed by the Roman Dictator, and expired with the Dictator's own office, typically a term of six months in the early and mid-republic. The served as the Dictator's main lieutenant. The Dictator nominated the , unless a specified, as was sometimes the case, the appointee. The Dictator could not rule without a to assist him, and, consequently, if the first either died or was dismissed during the Dictator's term, another had to be nominated in his stead.
The was granted a form of , but at the same level as a , and thus was subject to the of the Dictator and his powers were not superior to those of a Consul. In the Dictator's absence, the became his representative, and exercised the same powers as the Dictator. It was usually, but not always, necessary for the to have already held the office of . Accordingly, the had the insignia of a : the and an escort of six . The most famous Master of the Horse is Mark Antony, who served during Julius Caesar's first dictatorship, with disastrous results. As a result of this, Caesar appointed Marcus Aemilius Lepidus, who had a history of successful administration over the city of Rome and Hispania Citerior, to replace Antony and govern in Rome when Caesar went to suppress the renewed Civil War in North Africa.
After the constitutional reforms of Augustus, the office of Dictator fell into disuse, along with that of the . The title was revived in the late Empire, when Constantine I established it as one of the supreme military ranks, alongside the ("Master of the Foot"). Eventually, the two offices would be amalgamated into that of the ("Master of the Soldiers").
The title Constable, from the Latin or count of the stables, has a similar history.
Master of the Horse (United Kingdom)
The Master of the Horse in the United Kingdom was once an important official of the sovereign's household, though the role is largely ceremonial today. The master of the horse is the third dignitary of the court, and was always a member of the ministry (before 1782 the office was of cabinet rank), a peer and a privy councillor. All matters connected with the horses and formerly also the hounds of the sovereign, as well as the stables and coachhouses, the stud, mews and previously the kennels, are within his jurisdiction.
The practical management of the Royal Stables and stud devolves on the chief or Crown Equerry, formerly called the Gentleman of the Horse, whose appointment was always permanent. The Clerk Marshal had the supervision of the accounts of the department before they are submitted to the Board of Green Cloth, and was in waiting on the Sovereign on state occasions only.
Exclusive of the Crown Equerry there were seven regular equerries, besides extra and honorary equerries, one of whom was always in attendance on the Sovereign and rode at the side of the royal carriage. They were always officers of the army, and each of them was on duty for about the same time as the lords and grooms in waiting. There are still several pages of honour who are nominally in the master of the horse's department, who must not be confounded with the pages of various kinds who are in the department of the Lord Chamberlain. They are youths aged from twelve to sixteen, selected by the sovereign in person, to attend on him or her at state ceremonies. At King Charles III's coronation they assisted the Groom of the Stool in carrying the royal train.
The current Master of the Horse is Lord de Mauley.
Today the Master of the Horse has a primarily ceremonial office, and rarely appears except on state occasions, and especially when the Sovereign is mounted. The Crown Equerry has daily oversight of the Royal Mews, which provides vehicular transport for the Sovereign, both cars and horse-drawn carriages. Train travel is arranged by the Royal Travel Office, which also co-ordinates air transport.