The Lex Imperialis, known also as the Dictates Imperialis, is the legal code of the Imperium of Man which consists of a vast body of laws and codes that have been compiled over ten millennia. Believed to be the word of the Emperor Himself, for ten thousand Terran years the Lex Imperialis has held the balance between the Imperium's forces, all derived from the precepts of the original Lord Commander of the Imperium, Ultramarines Primarch Roboute Guilliman.
Following the Battle of Terra, when the Emperor sustained mortal wounds during His final confrontation with the Warmaster Horus aboard his flagship the Vengeful Spirit and His subsequent internment within the Golden Throne, Guilliman assumed the role of Imperial Regent. It was he who imposed the Codex Astartes upon his brothers, which saw the sundering of the Legiones Astartes into the smaller, thousand-man Chapters. This conciliatory gesture helped to keep the peace between the Space Marines and the Adeptus Terra. And it was Guilliman, in consultation with the great Adeptus Custodes Captain-General Constantin Valdor, who issued the Edict of Restraint, under which the Custodian Guard were expressly enjoined to remain on Terra as guardians of the Enthroned Emperor.
Imperial Law and the Adeptus Arbites
The laws of the Imperium are upheld by the Adeptus Arbites, the Imperial Adepta that serves as the galactic police force of the Imperium of Man, responsible for enforcing Imperial Law on all human-settled worlds. To aid their investigations, most Precinct Fortresses boast a Cogitator stack containing a massively abridged version of just a portion of those judgements and precedents that fall commonly into the Arbitrators' local purview. These rulings by Segmentae Judges, High Marshals and even the Lords Marshal themselves, are designed to expedite the work of an individual Arbitrator. This massive collection of Imperial laws, rulings and judgements alludes more literally to the Book of Judgement. Of course, the entire body of the law is vastly greater than a single volume; no individual could ever comprehend more than a tiny fraction. It has been painstakingly collated over the millennia, and includes the words of the Emperor Himself and every decree and ruling ever passed by the High Lords of Terra.
The most ancient articles are written on crumbling parchments, inscribed in unknown tongues by the nameless functionaries of a forgotten age. Every day a hundred new volumes of encoded holoscript and hand-illuminated lettering are added. Volume upon volume sits upon the endless rows of ornate bookcases that fill the Hall of Judgement on Terra. Every row is home to ten thousand volumes, the shelves soaring a hundred metres up towards the vaulted ceilings. Over the ages, the Hall has been expanded and extended many times, so that it is now an entire complex covering many acres, with miles of corridors, levels, and rooms. Scholars, scribes, and law lords pace the time-worn marble floors, while above their heads, on the narrow gantries and ladders that cover the shelf stacks like a spider's web, crawl legal assistants and low-ranking functionaries, searching through the detritus of judgement for solar weeks and months at a time to find just a single reference.
Every Adeptus Arbites Judge, at some point in his career, attempts a pilgrimage to the Hall of Judgement, there to study the full intricacies of the law. Many spend long Terran years there, for the most heinous, subtle, or far-reaching crimes often require a lengthy process of research to pass judgement. While the Dictates Imperialis are extensive, the huge volume of prior cases and sometimes contradictory rulings can make it difficult to determine the correct decision. In especially complex cases, it may take centuries to reach an outcome -- a Judge may spend his entire life deliberating, scrutinising, and trying to fathom out the issues, only to pass his work on, unfinished, for others to continue. Millennia later, though the accused are long dead, a ruling is finally made and justice must be meted out upon the distant descendants and those obscurely associated with the original transgressor.
The Imperium is a theocracy, and although the Arbites wield and police temporal authority, religious concepts make up the bedrock of Imperial Law. The Lex Imperialis holds that the Emperor rightfully expects service and obedience from every human being in the galaxy, and that within the Imperium that expectation is made manifest through the scripture of laws. To break the Lex Imperialis is not only to disobey a law of the government, it is to violate the immaculate and divine moral order those laws set out. This violation of a divine order is present in every crime the Arbites investigate, and once this is understood the need for harsh methods and stern penalties becomes clear. For the Arbites, there is no such thing as a petty crime.
This is also why the heresy of Abstractionism is so reviled by right-thinking Arbites. It places the flawed and hubristic whims of an individual above the clean, majestic structures of the Emperor's laws as made manifest through the due scripture of His servants. The letter of the law is immaculate -- to claim access to the spirit of the law is to claim equality with the Emperor, a crime and a blasphemy which no Arbitor should countenance.
There are a number of broad crimes the Arbites constantly find themselves fighting. There are crimes of destabilisation, committed on scales taking in whole planetary populations. These are the waves of anarchy that can break across a world from disobedient anger at Adepta rule, or the criminal loss of discipline in the face of disaster or famine. It can be panic at imminent or actual invasion, or a hive-, continent-, or planetwide religious fervour that skews the perspective of the masses and sees them in flagellant processions or hysterical mass confessions rather than keeping the wheels of the Imperium turning. Where a Planetary Governor cannot restrain their citizens the Arbites must take the lead and set the example, breaking rioters, crushing panics, and showing the mob the meaning of Imperial loyalty and discipline. Invariably, when the Arbites must take such action, the governor will be called to account for his or her loss of control, and few survive their verdict.
It is said the Lex Imperialis allows that crimes of destabilisation may arise from raw passions ineffectively contained. Crimes of sedition have no such mitigation -- they result from the cold and careful intention to strike at the perfect machinery of Imperial rule. Blasphemy, heresy, the spreading of freethinking propaganda, and the deliberate and knowing defiance of Arbites law are all crimes of sedition, as are physical and moral assaults on the instruments of Imperial rule. A mind capable of deliberate sedition could be capable of anything, and the punishments for it are ruthless and terrifying to contemplate.
To enforce every mandate within the Lex Imperialis is a nearly impossible task. These codices of law are so enormous and erudite that few individuals can claim to know all of their secrets or loopholes. Even the Judges of the Arbites must regularly confer with archive-savants and librarium cogitation engines in order to make their rulings. Working for the local planetary Enforcers or powerful nobles during the all-too-rare trials, the legal experts make up a group of rare legal minds. These steadfast scholars spend solar decades poring over the Lex Imperialis, learning its every nuance and interpretation.
Imperial Law and the Inquisition
The Inquisition is another Imperial organisation which is responsible for upholding the tenets (the spirit if not the letter) of the Lex Imperialis. This secretive organisation exists outside the standard administrative hierarchy of the Imperium of Man. The Inquisition acts as the secret police force of the Imperium, hunting down any and all of the myriad threats to the stability of the God-Emperor's realm, from the corruption caused by the Forces of Chaos, Heretics, mutants and rebels, to assaults from vicious alien species. However, the agents of the Inquisition are not collectively dictated or indoctrinated in any specific or cohesive way to carry out the performance of their duties, for it is their individuality, strength of mind and belief, and sense of personal responsibility which enables them to perform the dire tasks that are asked of them.
To further complicate matters, the Inquisition is divided into various factions of two broad camps. There are those traditionally dubbed "Puritans," and the factions that are referred to as "Radicals." Puritans uphold the law and dictates of the Emperor to the letter, as enforced upon the populace and servants of the Emperor at large where possible. It is they who uphold the widespread beliefs that permeate the organisations of the Imperium, and can be said to adhere to the traditional religious values as preached by the Ecclesiarchy and enshrined at the heart of Imperial Law. Radicals, in their favoured positions as Inquisitors, feel they are free to enforce the spirit and intent of the Emperor's Judgements, and it can be truly said that they see the methods they employ to be secondary to the execution of their duties and the achievement of their goals. They would be considered Heretics by the vast majority of Imperial citizens for their behaviour, but those Lord Inquisitors, as more knowledgeable and wiser observers, can see there are powerful arguments to support their views and methodology. In either case, extremism of one type or another must always be closely witnessed, lest it turn to self-destructive obsession.
- Inquisitor: Rulebook (RPG), pg. 6
- Dark Heresy - The Book of Judgement (RPG), pp. 7, 9, 14-15, 22, 38, 48
- Watchers of the Throne - The Emperor's Legion (Novel) by Chris Wraight