In this long epic poem, we find out about the coming of King Arthur.
After Aurelius and King Uther, Arthur became the king of England, and under his reign, the Round Table was established. Arthur also united all the princes of England under him. He also fought with the Romans, who were ruling over England.
Arthur is going to win Guinevere, the fairest lady of the land, as his wife. He goes to her father, King Leodogran with the request for her hand in marriage, using the fact that he is the son of Uther. Leodogran sends him to prove himself in a battle.
In the middle of the battle, Arthur saves one of his knights and gets proclaimed king by him. He and the knight become best friends. Later, Arthur wins the battle and sends his knights to Leodogran, telling him that he was victorious. King Leodogran asks his chamberlain to tell him whether Arthur is in fact Uther's son, and the man says that Merlin knows Arthur is Uther's son.
Leodogran sends for the knights and asks their opinions, and two of them say that surely Arthur is who he claims to be. Then, the third knight relates how Arthur was given to Merlin when he was born, and Merlin gave Arthur to one of King Uther's favorite knights to be cared for. After he grew up, Arthur was crowned by Merlin and given Excalibur by the Lady of the Lake.
Then, Leodogran lets Arthur marry Guinevere, and the king unites the tribes of England, fighting the Romans and driving out the heathens in twelve great battles.