User blog comment:123Action/A Year/@comment-4814726-20131107051411/@comment-5102537-20131109131349

Yes, it was a fight to death. This is what Morgana tells Derian, the champion:

MORGANA And Derían, no pity, no quarter. Do not hesitate for one second. Arthur Pendragon must die.

And this is what Arthur and Merlin are saying:

MERLIN Arthur, do you really think this is worth the risk? You're king now. Camelot needs you. Alive.

ARTHUR I don't know what will happen. But for the first time since I became king, I know in my heart I've made the right decision.

I too found it odd that Caerleon didn't trespass Camelot's borders sooner when Arthur was still Regent Prince. It was the same in "The Tears of Uther Pendragon" when Uther was under the mandrake root's influence. This actually wasn't a reason to have an easy job of attacking Camelot when, except for Uther, everything and everyone was still normal and the same. For some reason the show always claimed that only Uther prevented enemies (kings/kingdoms) from attacking. His presence may have been important to the morals of the people and the army, but the knights, the army and Arthur stayed the same nevertheless.

Maybe Caerleon thought that Arthur had to deal with his grief and was in a weak state after Uther's death, so he dared to test him. While Uther's grief resulted in rage and hatred, Arthur's grief might have thrown him into surrender.