The Antiquarti is a secret group within the Inquisition. Indeed, it is comprised of Radicals and their servants and allies who broadly co-align with the goals of the mysterious Inquisitor Thaddeus Hakk.
Hakk has scoured the Koronus Expanse in search of some unknown fate, and it is said that he and the other Antiquarti seek to unravel the secrets of the past in the belief that in doing so they will gain prescience of future events.
Far from a philosophical matter of learning from past mistakes, the Antiquarti hold that the universe is governed by an underlying pattern, and all that transpires must adhere to this unseen scheme.
Inquisitor Hakk and his peers are reported to have delved into the very darkest places of the Jericho Reach, and because many of them bear the Inquisitorial Seal, they have often done so alongside the Deathwatch and other forces of the Imperium.
However, it appears that there are certain missions and certain places that the Antiquarti prefer to undertake alone, lest others denounce them as Heretics, or worse.
Whatever secrets Inquisitor Hakk and his allies might be seeking in the depths of the Outer Reach, it is clear that he has earned the enmity of a number of other factions in the process.
There is no shortage of Inquisitors of the Ordos Calixis ready to denounce him, though to date he has somehow managed to fend off the overt censure of his peers. Perhaps far more dangerous even than the enmity of other Inquisitors is the fact that the Antiquarti have made an enemy in the form of the Aeldari Harlequins.
These utterly lethal alien war-dancers only rarely become involved in the affairs of Humanity, but when they do it is almost never for the benefit of anyone but the Aeldari. That the Antiquarti have earned such a foe suggests they have delved deep indeed into places barred to mortals since the dawn of creation itself.
Such intrusions bring Inquisitor Hakk and his Antiquarti compatriots into conflict with other factions in the Inquisition, not least of which is the Dead Cabal.
- Deathwatch: The Outer Reach (RPG), pg. 52