The Kaggath was an ancient, but rarely employed rite of the Sith. One part duel, one part large-scale dejarik-match, the Kaggath pitted Sith against Sith unto humiliation and death. The challenger sets the arena, whether a planet, a star system or the entire galaxy. The two combatants must then muster their full power bases to outwit and outmaneuver each other and defeat or win over each other's forces. When the Dark Lord of the Sith Tulak Hord fought and won his one and only Kaggath, he declared that the name of his opponent would be stricken from history--and his command was fulfilled. The Kaggath has the power not only to destroy an individual Sith, but to obliterate his entire legacy. According to Darth Thanaton, Marka Ragnos participated in a Kaggath during his rise, as well as Ludo Kressh later on. Two Dark Council members once fought a Kaggath that destroyed the Emperor's Citadel. The rest of the Dark Council executed them.
During the Cold War, Thanaton challenged the Lord Kallig to a Kaggath to finally destroy the allegedly corrupt Sith. As they dueled on Corellia, it became apparent that Thanaton would lose, so he chose to flee to Korriban to seek the aid of the Dark Council, breaking the rules of the ritual. Kallig followed Thanaton and finished the duel in the Dark Council chamber. Thanaton was left near-death before he was executed by Darth Mortis.