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|Karl Fritz used the power of the Founding Titan...to give birth to massive Titans. These were to act as both his shields and his spears.|
|— Willy Tybur recounting the past|
The Wall Titans (壁の巨人 Kabe no Kyojin?) were Abnormal Titans similar in appearance to the Colossus Titan, one of the Nine Titans. They possessed the ability of crystallization and existed in vast numbers composing the three Walls, before Eren Yeager freed them in the year 854 via unhardening the Walls.
In the year 743, King Karl Fritz used the power of the Founding Titan to create and command "tens of millions" of these Titans to create the three Walls (Maria, Rose and Sina) and protect the last Eldian territory on Paradis Island. The lack of sunlight inside the Walls has supposedly rendered them immobile ever since, although King Fritz "threatened" to release them and use them to flatten the Earth should Paradis Island come under attack.
These Titans were similar in appearance to the Colossus Titan in that both their surfaces were covered primarily in muscle tissue and lack skin (although the Colossus Titan typically had more bony tissue exposed around its face). Like the Colossus Titan, they all shared the long arms and elephantine feet necessary to support their structures. Each Titan varied slightly, most noticeably around the face; some possessed very defleshed faces, with little more than bare skulls, while others exhibited complete musculature. Their exact heights were unknown- and likely varied somewhat- but they were about the height of the Walls, which were 50 meters tall.
Like other Titans, the Wall Titans generated great amounts of heat, enough to emit large plumes of steam not unlike the Colossus Titan. They could use this ability both offensively and defensively, creating smokescreens and flash-boiling seawater to incinerate entire battleships. All Wall Titans possessed the ability to harden, although it was probable that they only did so because they were commanded to by the Founding Titan. This hardening was used to mold the surface of the Walls, with the Wall Titans acting as their central pillars. After they were released from the Walls, they ceased any measure of hardening.
Their speed on land was estimated to surpass that of a galloping horse. They were also capable of maintaining this speed in water, as the entire horde crossed the ocean between Paradis Island and the mainland within a few days.
Like the Colossus Titan, their sheer size and mass enabled them the capacity for great destruction; with a single step, a Wall Titan was capable of collapsing buildings and pulverizing humans underfoot. This physical ability, coupled with the sheer number of Wall Titans, was the basis for Paradis' main deterrence, the Rumbling.
In the year 743, after King Karl Fritz abandoned the conflicts of Eldia causing the Great Titan War, he fled overseas with the main branch of the Fritz royal family and remnants of the Eldian populace to Paradis Island, Eldia's last remaining undisputed territory. He used the power of the Founding Titan to create and order tens of millions of Wall Titans to form the three concentric Walls to protect the Eldians. The King sent a message to the people of Marley, demanding that the Eldians on Paradis Island must be left alone or else the Wall Titans would "flatten the entire Earth."
During the battle between Eren Yeager and Annie Leonhart in the Stohess District, Annie attempts to escape by climbing the Wall but is stopped by Mikasa Ackerman. However, she damages part of the Wall, and a huge chunk is torn off, revealing the face of a mysterious Titan.
The massive hole in the Wall is immediately noticed by Mikasa. The Titan within the Wall follows Mikasa's gaze, and Minister Nick calls for the immediate covering up of the Titan, as the sunlight might eventually awaken it. After Nick ignores Hange Zoë's questions about it, he is nearly thrown off the Wall by Hange, but still refuses to reveal any details he might know because of the Church of the Walls' secrecy.
After the surviving Survey Corps reach Grisha Yeager's basement, they learn from his books about the story of the formation of the Walls as it was told to the Eldian Restorationists by Dina Fritz.
During the festival hosted by the Tybur family, Willy Tybur tells the world of the truth about the Walls, the Great Titan War, and King Karl Fritz. He reveals that due to the King's vow of pacifism which prevents the Founding Titan from being used for war, the Wall Titans were never a true threat. However, due to a coup d'état in recent years, the military of Paradis Island have overthrown the previous royal government and rendered the King's ideology of peace ineffective. Now that the Founding Titan belongs to Eren Yeager, who is seemingly capable of using its powers despite not having royal blood, and without interference from King Fritz's will, the world is truly in danger of the Wall Titans for the first time. Eren himself admits this to be true.
As the Royal Government discusses Zeke Yeager's requests which were brought to them by the Anti-Marleyan Volunteers, Eren Yeager reveals he is able to activate the powers of the Founding Titan by coming into contact with a royal-blooded Titan. He also states that this method can be used to awaken the Titans within the Walls without invoking the vow of renouncing war.
After Kiyomi Azumabito arrives on Paradis Island, she divulges the rest of Zeke's strategy to save Eldia which involves unleashing some of the Titans inside the Walls to demonstrate its destructive power. The island would then need to keep that power in reserve for the next 50 years as Eldia advances technologically.
Following Zeke's encounter with Eren, Eren successfully frees Ymir from her enslavement and invokes the Founder to begin the Rumbling. The Walls crumble, and the Wall Titans begin to march under Eren's command to eradicate all life outside the island.  As they make their way towards the outside world, they inflict collateral damage in the areas formerly within the Walls, mindlessly demolishing buildings and killing civilians. Within a few days, the last of these Titans have left the cities of Paradis.
By the time the combined force of the remaining Survey Corps and Warriors reach the harbor, the Titans are long gone from Paradis, their plumes of steam having receded over the horizon. Hange Zoë predicts that the Titans would be able to reach the coast of Marley and annihilate the cities closest to Paradis in the span of a few days. As half a day is required to service the flying boat, they decide to replot their course towards Odiha to buy some time.
The Titans nearing the Marleyan coast eventually encounter a naval blockade: The Global Alliance Fleet. The battleships begin bombarding the horde, who are swimming just below the surface. Few shots land, and fewer still do lasting damage. The Titans easily bypass the blockade, and as they pass under the warships, they unleash bursts of heat, instantly boiling the seawater around them and scorching the ships' crew to death. A thick haze obscures the harbor, hiding the coast from the view of the artillerymen defending the land. As the smoke clears, the Wall Titans rise out from the water and the remains of the naval fleet. The land artillery begin their barrage, but to the soldiers' shock, it is ineffective as well. As the artillerymen desert their posts and retreat towards higher ground, they spot Eren's Founding Titan following the phalanx of Wall Titans.
As the Titans march, Eren recalls his mother's death, and the vow he made that day to keep pushing forward until he destroys every last one of his enemies. As he does so, the Wall Titans take their first steps on Marleyan soil, marking the beginning of the prophesied Rumbling.
The Wall Titans make their way further inland, eventually reaching the seaside town infiltrated by the Survey Corps some months before. Encircling the town via the mountains surrounding it, the Titans annihilate the settlement with the civilians who were unable to escape. As they leave the cratered remnants of the town, a youthful incarnation of Eren reminisces on his childhood: confined by the Walls and inspired by the descriptions of the outside world from Armin Arlert's book; his thoughts compounded with the spectacle of the Titans' carnage. He then states he has reached freedom, and, turning around, asks Armin's opinion of it through the Paths.
The Wall Titans continue their long march through the continent's interior, eventually nearing the port city of Odiha. As they lumber closer towards it, a lone soldier flies up to face them. The soldier is able to slay a few Titans, but succumbs to the intense heat of the Titans' bodies. The Titans proceed to crush Odiha underfoot.
As the Rumbling continues, the Wall Titans reach Fort Salta. Far from being defenseless, the airbase sends out airships in response to the Titans' arrival. The airships float high above the Titans, and as the base's commander addresses his men in the craft, the Attack Titan makes a sudden movement. Panicking, the commander orders the bombing to commence, to the protest of the airmen as they are too high to accurately drop their bombs. Consequently, the bombing does little to the advancing Wall Titans, and they continue marching as an apparition of the Beast Titan manifests and shoots the airships down.
Shortly after Zeke Yeager is executed by Levi Ackerman, the Wall Titans' steady march is abruptly halted near Fort Salta. Slumping and seemingly deactivated, they stand and kneel unresponsive. Soon after Eren Yeager's death, the Wall Titans vanish as the Power of the Titans has been relinquished by Ymir.
In Rikao Yanagita's analysis of the Attack on Titan manga, an estimation of the amount of Wall Titans residing within the Walls is given. Using the dimensions given in Attack on Titan: Before the Fall, Rikao estimates that, if the Wall Titans are all approximately 45 meters in height with a proportional 13-meter shoulder width with all Titans lined up shoulder to shoulder, there are approximately 246,000 Wall Titans within Wall Maria and a total of 585,000 Titans within all three Walls combined. This conflicts with information given much later in the manga in Chapter 86, in which King Fritz's ultimatum given to Marley states that he would unleash the "tens of millions of Titans that sleep inside the Walls" if war was declared against Eldia. Furthermore, Paradis Island's evident correlation with the real world island of Madagascar leaves no room for Walls of the sizes given in Before the Fall, meaning there may be even fewer Titans within the Walls than Rikao's estimate and Karl Fritz's claim.
- Taking Hange's estimate of the Wall Titans traversing 600 km of land in half a day, we can deduce that they are capable of sustaining 50 kph, indeed slightly faster than a horse's gallop.
- Despite being Pure Titans, none of the Wall Titans were seen reverting back into human form after the power of the Titans was sealed.