- "Those are brave men knocking at our door. Let's go kill them."
- ―Tyrion Lannister
The battle was an attempt by Stannis Baratheon to take King's Landing, the capital of the Seven Kingdoms, and to seize the Iron Throne from Joffrey Baratheon. It required a naval assault and an attack on the city gates by land. Tyrion Lannister, Acting Hand of the King, led the defense of the city. He successfully destroyed a large portion of Stannis's fleet through the use of wildfire, but was unable to prevent Stannis's army from landing and gaining the walls of the city. However, late-arriving reinforcements under Lord Tywin Lannister and Ser Loras Tyrell defeated Stannis's army, resulting in a decisive Lannister-Tyrell victory in King Joffrey's name.
Upon claiming the Iron Throne, Stannis Baratheon realised he lacked the manpower needed to take King's Landing. With the help of Melisandre, a red priestess from Asshai, he arranged the assassination of his younger brother, Renly, and secured the loyalty of many of the lords sworn to him. However, he failed to win the allegiance of House Tyrell, who withdrew their large army from the field and returned to Highgarden. Nevertheless, having also secured an alliance with the freesail captain Salladhor Saan, Stannis was confident of victory. On the advice of his loyal vassal and future Hand, Ser Davos Seaworth, he decided not to take Melisandre with him to King's Landing, concerned that the victory would be credited to her and not himself.
With King's Landing in danger, Tyrion Lannister made preparations to withstand siege. However, most of their manpower had been drawn north to fight the Starks in the Riverlands, leaving the city walls undermanned. Tyrion planned to level the field through the use of wildfire, a dangerous but highly destructive substance. With Robb Stark's forces poised in the west, Tywin was unwilling to leave his defensive position at Harrenhal, fearing being attacked from the rear. However, when Robb launched an invasion of the Westerlands instead, drawing close to Casterly Rock, Tywin decided to move his army. At the same time, Lord Petyr 'Littlefinger' Baelish negotiated a fresh alliance between House Lannister and House Tyrell.
- "Come with me and take the city!"
- ―King Stannis I rallies his forces
Stannis's fleet, commanded by Davos, swept into Blackwater Bay and approached the city. The original plan was to destroy the royal fleet and land troops under the city walls. However, the royal fleet proved to be absent, Tyrion having commanded it to leave the area (to Joffrey's incomprehension) rather than be sunk. Instead, Tyrion had a ship filled with wildfire and sent it to leak the substance directly into the bay. At his signal, Commander Bronn of the King's Landing City Watch ignited the wildfire with a flaming arrow. This resulted in a tremendous explosion that obliterated the leading elements of Stannis's fleet, including Davos' flagship.
Whilst the explosion sunk many of Stannis's ships, it was insufficient to stop him landing significant numbers of troops on the banks of the Blackwater Rush below the city. Under heavy arrow fire, Stannis personally led an assault on the city walls and managed to lead a small detatchment on the battlements. An attempted sally led by Sandor Clegane faltered due to his fear of fire and his flight from the field. Queen Regent Cersei recalled her son from the battlefield, leading to a loss of morale amongst the King's Landing defenders. Tyrion rallied them and led a counter-attack on a battering ram trying to smash down the Mud Gate, accompanied by Ser Mandon Moore and Ser Boros Blount of the Kingsguard. A late-arriving force of Stannis's troops attacked but was checked by Tyrion's forces. Tyrion's moment of victory was ruined when Ser Mandon turned on him and struck him down with a blow to the face, although Moore was in turn slain by Podrick Payne, Tyrion's squire.
At this point, Tywin Lannister's army arrived in concert with the Tyrell forces under Ser Loras. Ser Loras wore the armor and crown of the late Renly Baratheon to sow confusion and discord amongst Stannis's men. The reinforcements defeated Stannis's army, although some were able to retreat in good order to their landing vessels. Stannis was dragged reluctantly from the battlefield by loyal retainers.
The forging of an alliance between House Lannister and House Tyrell places the overwhelming bulk of the armies of southern Westeros under the banner of King Joffrey Baratheon. This combined army now hugely outstrips the armies of House Stark in size, and makes the Lannister-Tyrell faction the largest and most powerful in the war.
Based on information from previous episodes, it is known that Stannis's fleet numbers 200 ships, including 30 freesail vessels commanded by Salladhor Saan. They outnumber the royal fleet 10-1, indicating that the royal fleet in Blackwater Bay consists of just 20 ships. Only one - the ship laden with wildfire - takes part in the battle, the other nineteen having been sent out of the area on Tyrion's order.
Stannis's army consists of his own forces from Dragonstone and the surrounding islands, augmented by the forces he inherited from Renly. However, it is known that not all of the 100,000 troops under Renly joined Stannis, with House Tyrell's contingent withdrawing. In the TV series, no figure is given for how many troops withdrew and how many stayed with Stannis. Whilst we know that Stannis's troops outnumber the defenders of King's Landing 5-1, we don't know the precise numbers.
Also, whilst we know that Tywin Lannister's army in the Riverlands consisted of more than 30,000 troops, we don't know how many forces he left behind with Gregor Clegane to continue the fight and how many he took south to the capital.
Numbers for these figures are given in the books: Stannis attacked King's Landing with approximately 20,000 men, whilst the combined Tyrell-Lannister host was more than 100,000 strong. The defenders of the city numbered some 6,800 troops. It is not known how closely the TV series adhered to these numbers.
In the books
In the Song of Ice and Fire novels, the Battle of the Blackwater unfolds somewhat differently than in the TV series, although the general sequence of events is similar. The battle is the culmination and climax of the second novel in the sequence, A Clash of Kings.
In the novels, Renly's death was followed by Stannis seizing control of Storm's End, the ancestral Baratheon castle. Most of the lords of the Stormlands and a few of the Reach (those present) joined Stannis's cause, but the bulk of the Reach lords regrouped at Bitterbridge. Stannis assumed that Tyrells would swear to his cause, but the knights that went to parley with the Reach lords were imprisoned. Stannis sent his fleet into Blackwater Bay and his army by land northwards through the Kingswood. In the Kingswood, Stannis's army was harrassed and delayed by Tyrion's hill tribes, particularly the Stone Crows under Shagga, whom he had deployed as skirmishers.
Tyrion and Cersei initially hoped that Renly and Stannis would exhaust themselves fighting one another, buying time for their father to win a decisive victory over the Starks and then come to the relief of the city. However, with Robb Stark winning victory after victory (at Oxcross, Ashemark, the Crag and other engagements), this was not possible, forcing Tywin to remain at Harrenhal. Indeed, Robb's armies began threatening other Westerland strongholds, forcing Tywin to reluctantly march to meet Robb in battle or risk losing the confidence of his lords, whose homelands were now in peril. However, Edmure Tully sent a force from Riverrun to hold the fords over the Red Fork, delaying Tywin's forces long enough for him to hear that Stannis was on the march. He immediately turned his army south to the headwaters of the Blackwater Rush and built barges to transport his forces to King's Landing by river.
Hearing of the Tyrell reluctance to join Stannis, Tyrion dispatched Littlefinger to negotiate, authorising him to offer Joffrey's hand in marriage to Margaery Tyrell. The Tyrells accepted the offer and their army moved north to the Blackwater, meeting Tywin's forces as they came down the river. At the same time, Tyrion secured the city's unusually large stocks of wildfire and also began building an immense chain across the mouth of the river.
When Stannis's fleet arrived, the royal fleet engaged it in battle and drew it into the mouth of the river. Tyrion raised the chain behind Stannis's ships to prevent their escape and then detonated barrels of wildfire located under the river mouth, causing a conflageration that consumed most of Stannis's fleet (as well as the royal fleet). However, Tyrion did not appreciate that this would create so many burned-out hulks that, after a couple of hours, Stannis's army would be able to use them as an effective bridge to reach the city. Sandor Clegane and then Tyrion himself led sallies to defend the city, Sandor fleeing after the first and Tyrion being severely wounded in the second sortie by Ser Mandon Moore of the Kingsguard. As Tyrion passed out, the joint Lannister-Tyrell army arrived and destroyed Stannis's forces. Stannis, observing from the south bank of the river, was able to withdraw and evacuate to Dragonstone with several thousand troops.
The most notable difference between the TV and book versions of the battle is the absence of the iconic chain, the raising of which makes Ser Davos realise that he's sailed into a trap. In addition, in the novel the royal fleet is present and draws Stannis's fleet into the trap. Although some ships manage to escape upriver to escape the explosion, several royal galleys are sacrificed to the wildfire. In the novel, Stannis also does not personally take part in the battle and remains south of the river, making it much easier for him to escape once the tide turns against his forces. Another difference is that it is actually Ser Loras's older brother, Ser Garlan Tyrell, who wears Renly's armor as he is a better fit.
- The Battle of the Blackwater at A Wiki of Ice and Fire (major spoilers from the books).