The correct answer to this open question is the following.
The greatest legacy of King Arthur in the story the Day of Destiny is that King Arthur is the sense of loyalty and inspiration that he left in his people. In them, King Arthur will live forever.
"The Death of King Arthur" was written by Thomas Malory, pretending to be a reworking of the traditional stories of King Arthur and the main characters of the story such as Lancelot, Guinivere, Merlin, and the Knights of the Round Table.
In chapter 8, "The Day of Destiny," King Arthur kills his enemy Mordred at the Battle of Camlan but Arthur is badly wounded and die. One of his Knights, Bedivere take the spade -Excalibur- and put Arthur's body in a canoe that takes him to Avalon.