Camelot

In the opening scene, King Arthur (Richard Harris) is preparing for a great battle against his friend, Sir Lancelot (Franco Nero), a battle he does not wish to fight but has been forced into. Arthur reflects on the sad circumstances which have led him to this situation, and asks his childhood mentor, Merlyn, for advice. Merlyn appears to him and tells Arthur to think back.
Arthur thinks back to the night of his marriage to his now-estranged wife, Guenevere. It is an arranged marriage, and he has never met her before. He is understandably afraid of what lies ahead ("I Wonder What the King is Doing Tonight"). His solitude is broken by Guenevere and her entourage. Guenevere is also worried about marrying a man she has never met, and longs for an easier life ("The Simple Joys of Maidenhood"). Like Arthur, she flees from her entourage to reflect on her future. Arthur (overhearing Guenevere and realizing who she is) accidentally falls out of the tree in which he is hiding. He and Guenevere converse, as she does not know his true identity, and realize they have things in common. Arthur tells her what a wonderful place his kingdom is ("Camelot") and they almost kiss, but are interrupted by men sent to find Arthur. The king's identity is revealed, and although Arthur gives Guenevere the chance to leave she gladly goes back with him to be married.
The plot shifts to five years later. Arthur confides to Guenevere his idea for a "Round Table" that would seat all the noble knights of the realm, reflecting not only a crude type of democratic ideal, but also the political unification of England. Knights are shown gathering from all over England. The plot shifts another five years, and word of Arthur's Round Table spreads to France. Inspired by Arthurâs ideas, the self-righteous French knight Lancelot makes his way to England with his squire Dep, boasting of his superior virtues ("C'est Moi"). Lancelot's prowess impresses Arthur and they become friends, but many of the knights despise Lancelot for his self-righteousness.
Guenevere also dislikes Lancelot at first, and, to Arthur's chagrin ("How to Handle a Woman"), incites three of the best knights â Sir Lionel, Sir Sagramore, and Sir Dinadan â to challenge him to a joust ("Then You May Take Me To The Fair"). However, the plan goes awry as Lancelot easily defeats all three, almost killing Sir Dinadan (Sir Lionel in the stage version). A horrified Lancelot pleads for Sir Dinadan to live, and as he lays hands on him, Dinadan miraculously recovers. Guenevere is so impressed that her feelings for Lancelot begin to change. Soon afterwards, it is revealed that, despite his vows of celibacy, Lancelot is in love with Guenevere, leading to the famous love triangle involving Arthur, Guenevere, and Lancelot. Guenevere knows it is wrong and tries to get Lancelot out of her life, but he refuses to leave ("If Ever I Would Leave You"). Arthur realizes something is going on between Lancelot and Guenevere but cannot bring himself to alienate either of them, and so turns a blind eye. Mordred (David Hemmings), Arthur's illegitimate son from an affair with Morgause (Arthur's unknown half-sister in some versions of the legend), arrives at Camelot, bitter at Arthur's refusal to recognize him and determined to bring down the fellowship of the Round Table by stirring up trouble. All this takes its toll on Arthur's disposition, and Guenevere tries, but fails, to cheer him up ("What Do the Simple Folk Do?").
Mordred cunningly convinces Arthur to stay out hunting all night as a test, knowing Lancelot will visit Guenevere in her bedchamber. Everything happens as Mordred expected. Guenevere admits her feelings for Lancelot but still feels guilty ("I Loved You Once In Silence"). Mordred rouses several knights and they catch the lovers together, as he planned. Lancelot escapes but Guenevere is arrested and sentenced to die at the stake. Arthur, who has promoted the rule of law throughout the story, is now bound by his own lawâhe can make no special exceptions for his own wife. Preparations are made for Guenevere's burning ("Guenevere"), but Lancelot rescues her at the last minute, much to Arthur's relief.
In the filmâs final scene, we return to the opening. Arthur is preparing for battle against Lancelot, at the insistence of his knights who want revenge, and England appears headed into the Dark Ages. He suddenly receives a surprise visit from Lancelot and Guenevere, who has become a nun. Arthur and Guenevere share an emotional farewell. The battle must continue, however. Prior to the battle, Arthur stumbles across a young boy named Tom, who wishes to become a Knight of the Round Table. Arthur is skeptical at first, but Tom espouses his commitment to Arthur's original ideal of "Not might makes right, but might for right." Arthur realizes that, although most of his plans have fallen through, the ideals of Camelot still live on in this simple boy. Arthur knights Tom and gives him his ordersârun behind the lines and survive the battle, so he can tell future generations about the legend of Camelot. Watching Tom leave, Arthur regains his hope for the future ("Camelot (reprise)").

Question: Who is Arthur battling against?
Answer: Lancelot.