Merlin’s deepest roots are Welsh. The bardic tradition preserves Myrddin Wyllt ("Merlin the Wild"), a 6th-century North British prophet who lost his mind at the battle of Arfderydd and lived as a hermit in the Caledonian Forest, speaking in prophecy to the trees. Geoffrey of Monmouth fused Myrddin with the boy-prophet Ambrosius in the Historia Regum Britanniae (1136), naming him Merlinus and giving him the famous prophecies and the engineering of Stonehenge. Geoffrey’s later Vita Merlini (c. 1150) is a long Latin poem on the prophet’s wild-man years. The Vulgate Cycle (13th century) added the Tintagel conception, the sword in the stone, the founding of the Round Table, and the trap at Brocéliande.
The standard arc, in order, runs: the boy-prophet at Vortigern’s tower, where he reveals the red and white dragons sleeping under the foundations and prophesies the future of Britain; the raising of Stonehenge from Ireland by enchantment as a memorial to the British dead; the engineering of Uther’s shapeshift as Gorlois at Tintagel and the resulting conception of Arthur; the fostering of the boy at Sir Ector’s manor; the planting of the sword in the stone in a London churchyard at the New Year; the proclamation of Arthur as high king; the gift of Excalibur from the Lady of the Lake; the founding of the Round Table at Camelot; the long counsel through Arthur’s reign; the trap at Brocéliande, where Vivien (the Lady of the Lake) seals him into the air or the rock and leaves him to prophesy from inside it for as long as Britain stands.
For video, anchor each Merlin scene to a moment from the cycle and a specific source: the boy at Vortigern’s tower (Geoffrey, Historia VI.17), Stonehenge at the raising (Geoffrey, VIII.10), the candlelit Tintagel scene (Vulgate Estoire de Merlin), the sword-in-the-stone (Vulgate), the Brocéliande trap (Vulgate / Tennyson’s Idylls). Lean on the Welsh-into-medieval palette: forest greens of Brocéliande and Caledonia, slate of standing stones, blue of bardic robes, gold of the Tintagel candles, mist on stone. The more concrete the moment, the closer the output lands to the cycle.