When Aurelius Ambrosius was High King of Britain, Merlin, also called Ambrosius, brought the Giants' Dance out of Ireland and set it up near Amesbury, at Stonehenge. Shortly after this a great star appeared in the likeness of a dragon, and Merlin, knowing that it betokened Ambrosius' death, wept bitterly, and prophesied that Uther would be King under the sign of the Dragon, and that a son would be born to him “of surpassing mighty dominion, whose power shall extend over all the realms that lie beneath the ray (of the star).”
The following Easter, at the Coronation feast, King Uther fell in love with Ygraine, wife of Gorlois, Duke of Cornwall. He lavished attention on her, to the scandal of the court; she made no response, but her husband, in fury, retired from the court without leave, taking his wife and men-at-arms back to Cornwall. Uther, in anger, commanded him to return, but Gorlois refused to obey. Then the King, enraged beyond measure, gathered an army and marched into Cornwall, burning the cities and castles. Gorlois had not enough troops to withstand him, so he placed his wife in the castle of Tintagel, the safest refuge, and himself prepared to defend the castle of Dimilioc. Uther immediately laid siege to Dimilioc, holding Gorlois and his troops trapped there, while he cast about for some way of breaking into the castle of Tintagel to ravish Ygraine. After some days he asked advice from one of his familiars called Ulfin, who suggested that he send for Merlin. Merlin, moved by the King's apparent suffering, promised to help. By his magic arts he changed Uther into the likeness of Gorlois, Ulfin into Jordan, Gorlois' friend, and himself into Brithael, one of Gorlois' captains. The three of them rode to Tintagel, and were admitted by the porter. Ygraine, taking Uther to be her husband the Duke, welcomed him, and took him to her bed. So Uther lay with Ygraine that night, “and she had no thought to deny him in aught he might desire.”
But in the meantime fighting had broken out at Dimilioc, and in the battle Ygraine's husband, the Duke, was killed. Messengers came to Tintagel to tell Ygraine of her husband's death. When they found “Gorlois,” apparently still alive, closeted with Ygraine, they were speechless, but the King then confessed the deception, and a few days later married Ygraine. Some say that Ygraine's sister Morgause was married on the same day to Lot of Lothian, and the other sister Morgan le Fay was put to school in a nunnery, where she learned necromancy, and thereafter was wedded to King Urien of Gore. But others aver that Morgan was Arthur's own sister, born after him of the marriage of King Uther and Ygraine his Queen, and that Morgause was also his sister, but not by the same mother.
Uther Pendragon was to reign for fifteen more years, and during those years he saw nothing of his son Arthur. Before the child was born Merlin sought out the King and spoke with him. “Sir, ye must purvey you for the nourishing of your child.” “As thou wilt,” said the King, “be it.” So on the night of his birth the child Arthur was carried down to the postern gate of Tintagel and delivered into the hands of Merlin, who took him to the castle of Sir Ector, a faithful knight. There Merlin had the child christened, and named him Arthur, and Sir Ector's wife took him as her foster son.
All through Uther's reign the country was sorely troubled by the Saxons and the Scots from Ireland. The two Saxon leaders whom the King had imprisoned managed to escape from London and fled thence to Germany, where they gathered a great army which struck terror throughout the kingdom. Uther himself was stricken with a grievous malady, and appointed Lot of Lothian, who was betrothed to his daughter Morgause, as his chief captain. But as often as Lot put the enemy to flight, they came back in even greater strength, and the country was laid waste. Finally Uther, though sorely ill, gathered his barons together and told them that he himself must lead the armies, so a litter was made for him, and he was carried in it at the head of his army against the enemy. When the Saxon leaders learned that the British King had taken the field against them in a litter, they disdained him, saying that he was half-dead already, and it would not become them to fight him. But Uther, with a return of his old strength, laughed and called out: “They call me the half-dead king, and so indeed I was. But I would rather conquer them in this wise, than be conquered by them and live in shame.” So the army of the Britons defeated the Saxons. But the King's malady increased, and the woes of the kingdom. Finally, when the King lay close to death, Merlin appeared and approached him in the sight of all the lords and bade him acknowledge his son Arthur as the new King. Which he did, and afterwards died, and was buried by the side of his brother Aurelius Ambrosius within the Giants' Dance.
After his death the lords of Britain came together to find their new King. No one knew where Arthur was kept, or where Merlin was to be found, but they thought the King would be recognized by a sign. So Merlin had a great sword fashioned, and fixed it by his magic art into a great stone shaped like an altar, with an anvil of steel in it, and floated the stone on water to a great church in London, and set it up there in the churchyard. There were gold letters on the sword which said: "Whoso pulleth out this sword of this stone and anvil, is rightwise king born of all England." So a great feast was made, and at the feast all the lords came to try who could pull the sword from the stone. Among them came Sir Ector, and Kay his son, with Arthur, who had neither sword nor blazon, following as a squire. When they came to the jousting Sir Kay, who had forgotten his sword, sent Arthur back to look for it. But when Arthur returned to the house where they were lodging, everyone was gone and the doors were locked, so in impatience he rode to the churchyard, and drew the sword from the stone, and took it to Sir Kay. Then of course the sword was recognized, but even when Arthur showed that he alone of all men could pull it from the stone, there were those who cried out against him, saying it was great shame to them and to the realm to accept as king a boy of no high blood born, and that fresh trial must be made at Candlemas. So at Candlemas all the greatest in the land came together, and then again at Pentecost, but none of them could pull the sword from the stone, save only Arthur. But still some of the lords were angry and would not accept him, until in the end the common people cried out: "We will have Arthur unto our king, we will put him no more in delay, for we all see that it is God's will that he shall be our king, and who that holdeth against it, we will slay him." So Arthur was accepted by the people, high and low, and all men rich and poor kneeled to him and begged his mercy because they had delayed him so long, and he forgave them.
Then Merlin told them all who Arthur was, and that he was no bastard, but begotten truly by King Uther upon Ygraine, three hours after the death of her husband the Duke. So they raised to be king Arthur the young.