Battle of the Trident

The Battle of the Trident was the climactic battle of the civil war known as Robert's Rebellion.

Prelude
In his previous campaigns, Robert Baratheon had successfully led his main army north from the Stormlands to join his main allies in the North, the Vale and the Riverlands. He cut his way through loyalist Houses that attempted to stop him at Summerhall, Ashford, and Stoney Sept. At the last location, a loyalist army attempted to corner him but in the Battle of the Bells, the armies of the North, Vale and Riverlands arrived and their combined forces drove them off. The combined rebel army then withdrew into friendly territory north of the Trident. The Riverlords remained divided but House Tully sided with the rebels.

While the rebels massed north of the river, Crown Prince Rhaegar Targaryen - who had started the entire war when he abducted Lyanna Stark - finally reappeared in King's Landing and massed the bulk of the remaining loyalist forces. He then led them north to face off against Robert's armies when they attempted to cross south of the Trident and advance on King's Landing.

Robert's rebel army at the Trident was composed of the forces from the Stormlands, the North, the Vale, and rebel houses from the Riverlands such as the Tullys. Robert's personal army from the Stormlands was somewhat diminished in size from all of the fighting it had seen but was more battle-hardened. The rebel forces from the North, Vale, and Riverlands had also seen action at the Battle of the Bells and though slightly outnumbered by Rhaegar's army, had more combat experience. The army group was commanded by Lord Robert Baratheon himself, Lord Jon Arryn, Lord Hoster Tully, Lord Eddard Stark, and several of their bannermen, including Lord Roose Bolton of the Dreadfort, and Lord Thorren Forrester of Ironrath.

Rhaegar's loyalist army consisted primarily of the direct Targaryen vassals from the Crownlands, joined by 10,000 Dornishmen under the command of Prince Lewyn Martell of the Kingsguard. Rhaegar's own lawful wife was Elia Martell and the Mad King kept her as a virtual hostage in the Red Keep to ensure House Martell's support. A few men from the Reach were also present, but the bulk of House Tyrell's army was tied down further south besieging Storm's End, held by Robert's younger brother Stannis. Rhaegar's forces were fresh and larger than the rebel army but were unbloodied and less experienced. Prince Rhaegar Targaryen himself commanded the loyalist forces along with several of his most trusted Kingsguard, including Ser Barristan Selmy.

Battle
Prince Rhaegar Targaryen was slain by Lord Robert Baratheon during the battle resulting in a crucial and critical victory for the rebel forces. Rhaegar was killed at a ford in the river from a swing by Robert's warhammer, smashing the rubies from Rhaegar's armor with his killing stroke. This led to the site becoming known as the Ruby Ford.

Dorne lost 10,000 troops including Prince Lewyn Martell himself. Ser Barristan Selmy was severely injured and captured. Robert himself was also moderately injured in the fighting. Lord Roose Bolton counseled Robert after the battle to execute Ser Barristan but Robert overruled him and not only pardoned Selmy, but sent his personal maester to treat the grave injuries of Ser Barristan, recognizing the knight's courage and loyalty despite being on the enemy force.

In the Northern contingent, Lord Thorren Forrester of House Forrester was slain and his son Gregor Forrester became lord of the House.

Aftermath
The defeat marked the beginning of the end for the Targaryen dynasty. The main reason such a high number of Houses had remained loyal to the Mad King was because of loyalty they felt towards his son and heir Rhaegar. With Rhaegar dead, House Targaryen's popular support fell drastically. No army stood between the rebels and King's Landing, the only other loyalist armies being Mace Tyrell's army besieging Storm's End, and Tywin Lannister's marching from Casterly Rock towards the capital. Since Robert was wounded in the battle, it fell to Eddard to lead the rebel army south towards King's Landing, hoping to arrive before the Lannisters - who were presumably rushing to reinforce the capital city. What Eddard and Robert did not realize was that after the victory at the Trident and death of Rhaegar, Tywin had decided to betray the Mad King and join the winning side. The Lannister army arrived first, but after being let inside the gates they promptly turned on its defenders resulting in the Sack of King's Landing.

Lord Walder Frey, Lord of the Crossing and one of Lord Hoster Tully's bannerman, did not appear until the battle was done, for which Lord Tully nicknamed him "The late Walder Frey".

In the books
In the A Song of Ice and Fire novels, the Battle of the Trident took place at a ford over the River Trident several hundred miles north of King's Landing. The battle was only possible due to some impressive maneuvering by Lord Robert's army from the Stormlands, which had to travel through hundreds of miles of enemy territory to link up with the Stark, Tully, and Arryn forces north of the river.

The battle itself was on a large scale with Prince Rhaegar leading 40,000 loyalist troops. The rebels had slightly less, but the rebels were more experienced due to almost a year of warfare beforehand. The battle was quite bloody with high casualties on both sides, but in the end it was the loyalist force which broke and ran after Prince Rhaegar's death at the hands of Robert Baratheon. After Prince Rhaegar was killed, men on both sides stole the rubies that bejeweled his armor and crown.

The rebel side included the the main armies from the North and the Vale. Robert's army from the Stormlands had to fight its way north and was much diminished, but the remaining soldiers were battle-hardened veterans. The Riverlords were split between the rebels and loyalists, though the Tullys fought on the rebel side. House Darry, in contrast, were a major Riverlands House that fought on the Targaryen side.

The bulk of the loyalist army was composed of the full strength of the Targaryen bannermen in the Crownlands, augmented by 10,000 Dornishmen. This was supported by several loyalist Riverlands Houses and surviving loyalist armies from previous battles such as the Battle of the Bells. There were a few men present from the Reach and House Tyrell at the battle but the bulk of the Tyrells' army was tied down at the Siege of Storm's End away to the south.

As for the overall course of the battle, at one point Prince Lewyn Martell led the 10,000 strong Dornish contingent in an advance which threatened to break the rebel army's left flank. During the fighting he became badly wounded, however, and in the confusion Ser Lyn of House Corbray led a counter-charge by the rebels which halted the Dornish, and personally killed Lewyn. The vain and arrogant Ser Lyn would in later years boast about how he had personally defeated Prince Lewyn, though in reality Lewyn was already very badly wounded (perhaps mortally so) and Corbray simply finished him off.

Other notable characters present at the battle included Lord Jon Arryn, Lord Hoster Tully, and Lord Roose Bolton. The latter, following the rebel victory, suggested that Ser Barristan Selmy be killed, but Robert was so impressed by the valor and loyalty that Barristan had shown in the battle that he spared his life, even sending his own maester to tend to Barristan's wounds instead of his own, which were less serious. After the war, Robert even made Barristan the Lord Commander of his own Kingsguard. Robert's own injuries however led him to give command of the rebel army to Eddard Stark, who pursued the defeated loyalists south towards King's Landing, expecting to have to lay siege to the capital, only to find the armies of the Westerlands had already taken the city by treachery.