Forge Challenger Medallions from Cabal Gold to challenge Caiatl's chosen warriors in Battlegrounds.
The hammer must be equipped to acquire Cabal Gold.
Currently, our crypto-archaeologists cannot pinpoint the date of Calus's rise to power within the Cabal Empire. Like much of the Cabal Empire's ancient history, many dates and facts were altered to cast a favorable light upon the former emperor and his rise to power. Most of the Cryptarchy's information comes from post-Calus records, scoured from archival remnants on Red Legion vessels and forays into the Leviathan. As such, this record's historic context must be marked with an asterisk for questionable accuracy.
According to excerpts from the Cabal legal record known as the Codex of Lawful Transgressions, the Hammer of Proving dates back to the Foundation Age of Emperor Calus's reign. During this era, Cabal society was dominated by militaristic ambition centered around conquest and imperial expansion. As Calus took control of the empire, he sought to steer the Cabal people toward a society of art and philosophy (though this degenerated into decadence and debauchery).
In the early Foundation Age, the Rite of Proving was the primary means by which disputes were settled among free Cabal (much like how the Crucible was formed among the Guardians of the Last City). During the Proving, two Cabal or their appointed representatives would air their grievances in a public forum and one or both Cabal would declare a challenge. These Cabal would battle one another to submission or to the death—often the latter—and the winner would be seen as the right and lawful party in the dispute.
Calus disapproved, but knew that overturning a centuries-old tradition would be an unpopular decision. Instead, the emperor introduced incrementally draconian and byzantine bylaws into the Proving. One of these stated that if a battle ended with a tie or double-submission, an "impartial" imperial arbiter would decide the outcome. This arbiter would carry a symbol of Imperial office: a gold-plated hammer etched with strange runes drawn from Calus's own personal occult obsessions. The Hammer of Proving.
Whereas an impartial arbiter was a widely accepted change to the tradition, Calus abused it to push his own agenda. Over time, the Proving arbiter was granted more and more autonomy to settle battles, eventually gaining the right to enter a battle on their own under a number of flimsy justifications such as balancing "unfair" matches, ending matches that went "overly long," or punishing a Proving participant who owed a financial debt to the empire.
The Proving arbiter became such a disruptive force that within a century, the Rite of Proving had fallen out of common usage, as the law and restrictions around the Rite made it an untenable solution. Ultimately, the role of Proving arbiter was retired and the hammer returned to Calus's vaults.
During Caiatl's rise to power, she sought to win over those who had been put off by her father's cynical interpretations of Cabal tradition. Her regime reinstated the Rite of Proving as a simple combat challenge without arbiters or other superfluous trappings, and her adherence to custom gained her the steadfast loyalty of many influential warriors and politicians. This small army of dedicated followers is credited with easing her transition to a place of authority where her self-chosen honorific "empress" seems reasonable.
It is unknown how the Red Legion came into possession of the Hammer of Proving, but the weapon carries a significant historic weight to the Cabal people, one that can be leveraged as both an olive branch and—perhaps most fittingly—a bludgeon, depending on the wielder.