Trying to descibe Paladins as a concept within the rank structure of an early medieval society, or even a military is a somewhat tricky request as they're not a 'class' of soldier or even an organisation. The Paladins are a very specific (to an extent) group of heavily mythologised individuals somewhat analgous to the later Arthurian Knights of the Round Table, and indeed many Arthurian legends are based on the contemporary Chansons de Geste which feature the Carolingian Paladins. It is somewhat like asking how a soldier could become Sir Bedevere.

The Paladins appear in the Chansons de Geste - literally Songs of Deeds - which form a significant corpus of Early Medieval Frankish, later more widely European, heroic literature. The Chansons purport to be vaguely biographical, but their main purpose is essentially moral reinforcement by means of entertainment through the lens of Christian moralising. As with the Arthurian knights, a wider ensemble is implied but the main 'cast' as such features roughly twelve main 'characters'. These are a small cadre of knights who serve as military champions, heroes and companions of Charlemagne, chief amongst which is Charlemagne's cousin, Roland. Their deeds include protecting the Emperor, accompanying him on pilgrimmages and offering council, leading military campaigns, and the aggressive defence of the Church through actions such as recapturing relics.

The Song of Roland is perhaps the most famous of the Chansons de Geste and one of the most definitive sources for looking at the Paladins. Like Mallory's later Morte d'Arthur, the Song of Roland examines themes around self-sacrifice, bravery and betrayal. As with many things, the original was outstripped by its successors, and while the Arthurian legends burgeoned following Mallory's work and an extensive 19th Century revival, the original Chansons of the Paladins have faded into more obscurity.