Arthur's World or Morgaine's continuum was a mythic-seeming alternate Earth where advanced technology developed alongside magic.

Unlike other alternative timelines, Arthur's world was a natural alternative that had sprung from the universe. (PROSE: No Future) On this Earth, King Arthur was a historical British king and not merely a shadowy figure of myth. It produced several exceptional sorcerers (or users of advanced psychic powers).

Arthur ruled here before his overthrow (and probable killing) by Morgaine and her son, Mordred. Morgaine imprisoned Merlin, a version of the Doctor himself, leaving the knight Ancelyn, loyal to Arthur, and others to survive. Ancelyn knew of TARDISes and recognised the Doctor's seventh incarnation, though not by his face. The Doctor theorised that one of his future incarnations would move to Arthur's world. This incarnation left a note for him. (TV: Battlefield)

The Doctor had, however, earlier met another version of Merlin.

Arthur's World was accessible from the Doctor's universe, though possibly only if a certain ritual is performed linking the two worlds. The exit point in the main timeline is located in Carbury near Lake Vortigern, in rural England. Ancelyn told Brigadier Winifred Bambera that cars did not exist on Arthur's world. However, flying machines called ornithopters were used as transport (a helicopter being like one of these, only with whirling blades instead of wings).

This universe had at least Thirteen Worlds, all dominated by Morgaine, and the S'rax were the soliders of this universe. There may have been several stars as well, since Morgain was called "the Sunkiller." (TV: Battlefield)