The War Between Cornwall and the Sessoynes is a conflict over Cornwall’s survival and its tribute, but its decisive turn depends on a strained family bond: King Mark must seek the aid of Sir Tristram, the knight he hates, and Tristram chooses to defend him anyway. The fighting first brings Cornwall close to defeat; Tristram’s return changes the balance, and his victory over Elias ends the enemy’s claim to yearly tribute. It leaves the deeper danger untouched, since Mark’s hostility and Tristram’s trust persist after the battle.

Causes and the threat to Cornwall

While Sir Tristram is taking part in jousts and tournaments, he is seriously wounded, though he continues to win distinction. He goes to recover at the castle of Sir Dinas the seneschal. Meanwhile, a large force from Sessoin enters Cornwall and approaches Tintagil Castle under the command of Elias, a capable warrior. King Mark is unwilling to summon Tristram because he hates him, but his council warns that the enemy cannot be overcome without Tristram’s help. Faced with the prospect of losing the country, Mark reluctantly sends for his nephew.

Tristram answers the first summons with a limit: his wounds mean that he cannot bear arms for eight days. Mark accepts this and prepares to meet the Sessoynes with his own forces. The resulting battle is costly. Mark divides his army among Sir Dinas, Sir Andred, and Sir Arguis; Dinas performs notably, but Mark’s side is driven back toward Tintagil, suffering heavy losses as the enemy presses close to the gates. Mark then sends for Tristram again. Tristram says he will come when he has recovered, because until then he cannot help effectively.

Tristram returns and takes command

Once recovered, Tristram gathers ten good knights of Arthur’s court and rides to Tintagil. He approaches by woods and ditches and fights his way into the castle, where his arrival is welcomed by Mark and the company. The next morning, Elias challenges Mark to come out and fight. Mark turns to Tristram for counsel, and Tristram asks permission to answer the challenge and direct the battle. Mark grants him both.

Tristram arranges the defence in six divisions, placing Dinas in the vanguard and assigning other knights to command the rest. That night, he burns the Sessoynes’ ships, cutting off their apparent means of escape. Elias recognizes the purpose of the act and urges his men to fight without losing heart. In the battle that follows, Dinas’s division is driven back before Tristram enters the fighting. Tristram strikes down opponents and helps turn the contest, while the engagement moves back and forth between the open ground and Tintagil’s gates.

The confrontation remains uncertain even after Tristram’s intervention. Elias knocks Mark from his horse, and Dinas helps him remount. Tristram then meets Elias, who is also forced from his saddle. Fighting continues until nightfall. Mark returns to Tintagil having lost a hundred knights; the Sessoynes have lost two hundred. Both sides attend to their wounded, and neither appears eager to resume a general battle if it can avoid further loss and preserve its honour.

Elias’s challenge and the single combat

With his men dead and both armies reluctant to fight again, Elias proposes a contest between champions to settle Cornwall’s tribute. If Elias defeats Mark’s champion, the Sessoynes are to receive the tribute yearly; if their champion loses, Elias’s claim is to be relinquished for ever. Mark consults his barons, who consider a champion’s combat preferable to another full battle. They also acknowledge that Tristram’s prowess had been what enabled them to escape destruction.

Mark explains the proposal to Tristram, but does not ask him to fight, recognizing that Tristram has already saved their lives. Tristram nevertheless offers his help, provided he can act without forfeiting his honour or life. Though still bruised, he accepts Elias’s challenge. He identifies himself as Tristram, a knight of King Arthur and of the Round Table, and requires the two sides to make the terms secure. The agreement provides for a contest first on horseback and then on foot, continuing to the finish; hostages are given by both sides to ensure that the outcome will be honoured.

The duel and its consequences

The two knights meet in the field outside Tintagil. After their horses fall, they continue on foot. At first Elias has the advantage, and the spectators on Mark’s side fear that Tristram is beaten. Tristram remembers his lady, La Beale Isoud, and the possibility that he may never see her again; he raises the shield that had been hanging low and renews his effort. The reversal is visible to both armies: Mark’s followers, who had been grieving, begin to rejoice, while the Sessoynes’ confidence gives way. Tristram eventually overcomes Elias, who falls and dies. Before Elias’s death, Tristram recognizes him as a formidable opponent, second in his experience only to Sir Launcelot.

After the duel, Elias’s followers withdraw. Mark takes prisoners to compensate for the damage inflicted on his people and sends the others home to ransom their companions. Tristram is attended to and healed. The contest has settled the political stake established by Elias’s offer: the Sessoynes’ claim to Cornwall’s yearly tribute is ended. The result follows from an agreed combat between champions rather than another battle between the armies, with hostages intended to make the settlement binding.

The unresolved breach between Mark and Tristram

The victory does not reconcile the king and the knight. Mark still wants Tristram dead, despite the defence of Tintagil and the defeat of Elias. Tristram, for his part, does not learn from Mark’s conduct to guard against his treachery. He continues to remain where La Beale Isoud is, the personal attachment that had returned him to the fight also keeping him close to the danger posed by Mark.

The episode therefore closes with a divided consequence. Cornwall is rescued from invasion and its tribute claim is removed, but the alliance that made that rescue possible is not secure. Tristram’s service proves indispensable precisely where Mark’s feelings make him least willing to rely on it; his victory repairs the kingdom’s immediate peril without repairing the king’s hostility.