Knights of the Undying Crusade
The Knights of the Undying Crusade were a chivalric order of horse-riding knights based out of the Free City of Arbitrium before it fell to Ossiarch Bonereapers. Presumably, the order fell with the city.
Age of Sigmar
When Vigil Stormstroke and his army of Azyrite Arbiters arrived in Arbitrium to overthrow the Elder Counts, a number of those blood thralls who lived in luxurious comfort as slaves to the Counts cast aside their serfdom and stood with the Stormcast Eternals. These were the ancestors of the Knights of the Undying Crusade.[1a]
Ever since then the mortal champions of the order have defended the city, even during its vassalization under the Empire of Ossia.[1a] They often served as escorts for the lords and ladies of Arbitrium's Conclave, even to meetings with the Ossiarch Bonereapers.[1b]
When Margrave Nestira Suthura announced that Arbitrium would no longer pay the Bone-tithe, the knights of the order were among those who joined her rebellion.[1c] Despite their valiant efforts in the battle that followed, the city fell and most of its populace were slaughtered. The order likely fell with the city.[1d]
By tradition none are allowed to know the name of the Lord-Commander, except for the dead and undying.[1b] They were also known to carry ceremonial lances, though during the time of vassalization to the Empire of Ossia none could wield such weapons in battle, as the Ossiarchs took an arm from every citizen of the city for their Bone-tithe.[1b]
Knights of the order traditionally wore robes.[1a]