The Arthurian cycle has Brittonic Celtic roots. The earliest mentions are in the Welsh Y Gododdin (a 7th-century poem that compares a hero "though he was no Arthur"), the 9th-century Historia Brittonum (which lists Arthur’s twelve battles), and the medieval Welsh tales of the Mabinogion (Culhwch and Olwen, The Dream of Rhonabwy). Geoffrey of Monmouth wrote Arthur into a continuous Latin history of Britain in 1136, inventing the basic shape: Arthur the son of Uther Pendragon, conceived at Tintagel through Merlin’s magic, crowned high king of Britain, victorious against Saxons and Romans, betrayed by his nephew Mordred, mortally wounded at Camlann, carried to Avalon. Chrétien de Troyes (c. 1170–90) added Lancelot, Perceval, and the Holy Grail. The 13th-century Vulgate Cycle systematised the lot. Malory in 1485 closed the canon for all anglophone readers since.
The standard cycle, in order, runs: the conception at Tintagel; the boy Arthur drawing the sword from the stone in a London churchyard at the New Year; the gift of Excalibur from the Lady of the Lake at the lake-bank; the founding of Camelot and the Round Table; the marriage to Guinevere of Cameliard; the long fellowship of the Round Table knights (Gawain, Lancelot, Percival, Bedivere, Kay, Tristan, Galahad); the Quest for the Holy Grail (only Galahad attains it, only Percival survives intact); the love of Lancelot and Guinevere uncovered, splitting the fellowship; the rebellion of Mordred; the final battle at Camlann where Arthur kills Mordred and is mortally wounded; Bedivere casting Excalibur back into the lake on Arthur’s order; the barge of three queens carrying Arthur across to Avalon to be healed against the day Britain calls him back.
For video, anchor each King Arthur scene to a specific moment from the cycle and a specific source: the sword-from-stone (Vulgate Merlin), the gift of Excalibur (Malory I.25), the wedding feast in the great hall of Camelot, the Round Table at full session, the Holy Grail vision in the candlelit hall, the duel with Mordred at Camlann, Bedivere on the lake bank casting the sword. Lean on the late-medieval / early-Arthurian palette: pre-Raphaelite jewel tones, Burne-Jones gold leaf, illuminated manuscript blue and crimson, real Welsh hill-fort grey, mist over still water. Avoid Hollywood plate armour. The more concrete the moment, the closer the output lands to the cycle.