When Uther died, he had no heir. Merlin the wirzard put a sword caled Excalibur in a stone as a test to find the tru heir. Many men tried to draw the sword out of the stone, but only one succeeded. It was Arthur, so he became King of England.
When he married Guinevere he receved the rond table as a dowry. He sat at the table with his knights. He won many battles agains the Romans thanks to his knights.
Then Arthur and his knights undertook the Quest for the Holy grail and they had to stay away for a long times. On their return, Arthur learnt that Guinevere was in love with Lancelot. She fled to France with him That. ' s why he put his cousin Mordred in charge of the kingdom and left for France.
Arthur was fighting Lancelot in France when Mordred rebeled (tried to steal the thron ), so Arthur had to return to England to fight Mordred.
Finally, he fougt Mordred and killed him, but he died too.