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Warhammer 40K: The Adeptus Arbites – The Thin Black Line

6 Minute Read
Jul 15 2022

Learn of the men and women who walk the beat for the Emperor of Mankind – the Adeptus Arbites. It’s a tough job but someone has to do it.

The Adeptus Arbites are the police force of the Adeptus Terra, devoted to enforcing Imperial law throughout the entire Imperium. Utterly dedicated and without mercy, the Arbites are feared throughout the galaxy, for they are the agents of a harsh law, where failure and incompetence are crimes, and the only punishment is death. Arbites are empowered to act as judge, jury and executioner – citizens have no rights, and only members of the Priesthood of Terra or the Inquisition could claim anything so elaborate as a trial.



The Adeptus Arbites enforce the Lex Imperialis, embodied within the great Book of Judgement. Their organisation represents the soldiers and police of the Adeptus Terra. Each of the Imperium’s worlds have their own government, laws, and their own local police forces to enforce those laws. The Arbites concern themselves only with the enforcement of the broader laws to which the entire Imperium is subject. The common duty of the Arbites is overseeing that the Governor of each world is regularly paying his planets Tithe. In the event of a rogue Governor or a major revolt which threatens Imperial rule, the Arbites will brutally intervene to restore order. As a result of their constant oversight the presence of Arbites are often a source of discontent for Governors, but something they must nonetheless tolerate.

Symbol of the Adeptus Arbites


The Adeptus Arbites date from at least the Great Crusade, when compliant worlds had Lord Marshal‘s Offices installed to deal with ‘non-local’ matters.

During the Horus Heresy, the Grand Provost Marshal of the Arbites was part of the War CouncilDuring the War of the Beast, the significant Arbites garrison on Terra saw heavy action against the Ork Attack Moonover the Throneworld. The Arbites took catastrophic losses in the failed Proletarian Crusade, and its surviving Terran contingent struggled to maintain order on Terra as upheavals caused by the Greenskin presence broke out.

During the Age of Apostasy, the Adeptus Arbites fell under the control of Goge VandireFollowing The Blackness, the Arbites struggled to contain the situation on Terra as Chaos Cults activated across the planet and billions more of starving and maddened citizens rioted. Ultimately, most of the Arbites stations were overrun as only the Imperial Palace complex remained secure. Order was eventually restored following the Battle of Lion’s Gate and the arrival of Roboute Guilliman.The Arbites later aided Guilliman in his purge of Imperial bureaucracy that became known as the Primarch’s Scourge.

Organisational Structure

The overall leader of the Adeptus Arbites is the Grand Provost Marshal, who represents the organization on the Senatorum Imperialis and oversees the organization at the Hall of Judgement on Terra. Below him are the Marshals of the Court which oversee galaxy-spanning precincts. Below the Marshals of the Court, the Arbites are internally divided into two subgroups; Judges, who deal with legal matters and the application of ten thousand years of case law and its precedents, and Arbitrators, the militant arm of the Arbites who perform the work necessary to apprehend and punish those who break the Emperor’s laws. Senior Arbites fulfill both roles, with Judges getting their hands dirty, and Arbitrators learning to preside over lengthy court trials.


Arbites Precinct-Fortress

The Adeptus Arbites maintains a presence on almost every Imperial world, headquartered in fortified Precinct-Fortresses also known as Courthouses. The courthouses are equipped to be self-sufficient and to support a complete Arbites army. They consist of armouries, dungeons, barracks, firing ranges, scriptories, archives, warehouses, kitchens, gymnasia and garages. Courthouses are sometimes a world’s only connection with the rest of the Imperium.

FemalearbiterArbites Arbitrator


The men and women of the Adeptus Arbites are utterly devoted to their task and without mercy to those who break the Lex Imperialis. Arbites are usually recruited through the Schola Progenium, often favoring those who have displayed great force of will and brute strength.


Adeptus Arbites Equipment

The Adeptus Arbites are equipped to fight a minor war, but their main role is maintaining order. A single precinct courthouse functions as a base for a complete and fully-equipped army, capable of fielding vehicles. In combat Arbitrators wear carapace armour. Heavy gloves and boots protect the hands and feet, while the head is encased within an all-enclosing helmet equipped with a rebreather.

Standard personal weaponry is the Arbites combat shotgunboltgungrenade launchersuppression shield and the power maul. Several types of grenades are used, both lethal and incapacitating. Some Patrol groups and Enforcers may use Cyber-Mastiffs to hunt down and catch criminal fugitives who attempt to escape. The Arbites also make use of a wide range of vehicles, such as RhinosRepressors, and Chimeras. They also make use of Tarantula automated turrets for crowd control, riot suppression, and defending their precincts.

Adeptus Arbites Shock Baton

This weapon expands with a flick of the wrist from a small, easily concealable rod no longer than the width of a hand to a slim eighteen-inch long club. The weapon contains a tiny shock generator that can generate five Shock discharges before it requires recharging. It is common amongst undercover investigators who wish their quarry to survive for interrogation, and occasionally finds its way into the armouries of more secretive organisations like the Inquisition.


Adeptus Arbites Vox-Legi Patern Combat Shotgun

Effectively a large-bore, locally manufactured version of the shotgun designs used by many planetary enforcers, the Vox Legi is a devastating and adaptable weapon that fires shotgun shells nearly the size of those of Astartes Assault shotgun. The increased size of the weapon reduces its ammunition capacity compared to that of its fellow shotguns, but it still remains more powerful and adaptable than a standard shotgun. Most patrolling Arbitrators take advantage of this flexibility by carrying a variety of shotgun shell types so as to offer them different tactical options in the event of encountering a situation that requires their intervention. Over-engineered by a considerable margin, the weapon is also perfectly capable of being used as a large club in close combat. It is also designed for maximum psychological impact, with a very audible pump action (standard Arbites riot training makes use of this). The sound of a hundred Arbitrators simultaneously chambering their weapons has ended countless riots over the millennia. This pattern of combat shotgun is particularly widespread amongst the Arbitrators of The Periphery, and is broadly typical of the weapons favoured by Calixian Arbitrators.

Arbites Punisher class Strike Cruiser

Arbites Spacecraft

The Arbites also maintain a small fleet of patrol craft and counter-insurgency vessels, most notably among these the Punisher Class Strike Cruiser. The Arbites fleet also operates logistical vessels, transports, and other support craft.

Learn More of the Adeptus Arbites



“Remember that it is the duty of the mighty Adeptus Astartes Chapters and the glorious Imperial Guard to wage the Emperor’s wars and the duty of the fearless Imperial Navy to guard the Emperor’s spaceways, but it is to his loyal servants the Adeptus Arbites that His Divine Majesty in His infinite wisdom entrusts the most sacred duty of all – Keeping in check the lawless heretic rabble that passes itself off as the Emperor’s worthy subjects.”
– Familiar Arbites precinct-house joke

To serve the Emperor. To protect His domains. To judge and stand guard over His subjects. To carry the Emperor’s law to all worlds under His blessed protection. To pursue and punish those who trespassed against His word.
– Oath sworn by cadets

~Halt Citizen, I AM the Lex Imperialis


Author: Larry Vela
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