<P> Eren is introduced as a hot - headed, vocal ten - year - old in the town of Shiganshina who dreams of joining the Survey Corps in order to explore the outside world beyond the walls, but is constantly chastised by his mother Carla . A year prior to the events of the story, accompanying his father to meet her parents, Eren helps Mikasa Ackerman in dispatching her captors while developing his ideology . When the Titans invade Shiganshina, Eren is forced to watch his mother being devoured by one of the Titans and since vowed to kill every Titan henceforth . Enlisting in the military, Eren eventually places fifth overall in his graduating class . But between Shiganshina's fall and his enlistment in the military, Eren has vague memory of seeing his father Grisha as he is entrusted with key to the basement of their house before being injected with a mysterious liquid . </P> <P> During his first mission at Trost, Eren helps in the attempt to quell the Titans entering through the compromised wall before he is swallowed by a Titan when he sacrifices himself to save his friend Armin Arlert . But Eren suddenly transforms into a 15 - meter class Titan that rips his way out and attacks the other Titans to the humans' shock before he emerges from his Titan form . Though he is distrusted initially by the military despite sealing the wall, especially due to his inability to control himself in Titan form, Eren earns a place in the Special Operations Squad, a branch of Survey Corps under Levi assigned to watch over him . Shortly after joining, Eren finds himself hunted by a female Titan who kills all of his squadmates to get to him . With help of Levi and Mikasa, Eren is saved from the Titan who is later revealed to be his classmate Annie Leonhart . Though Eren defeats Annie alongside his allies, they are unable to get answers as they watch her encase herself using her Titan form's hardening ability . Eren soon learns during a mission to reach Krista Lenz, revealed to be Historia Reiss, that their other classmates Reiner Braun and Bertolt Hoover are the human forms of the Armored and Colossal Titans who were responsible for the Shiganshina attack . </P> <P> It was then that Eren learns he possess a power that the enemy Titan Shifters seek called "The Coordinate", subconsciously directing a group to kill and devour the Titan that killed his mother and then has them attack Reiner and Bertolt so he and his friends can fall back . After being rescued, Eren is sent with his friends to an isolated village while preparations are made for a campaign to retake Wall Maria for good, by making use of his newfound power . But Eren is then captured by the royal family's patriarch Rod Reiss, who reveals the "Coordinate" was originally in his family for years since their founding ancestor created the walls until it was stolen . Eren also learns that his transformation into a Titan was caused by Grisha, another Titan Shifter, whom he unconsciously devoured to inherit "The Coordinate" which Grisha obtained from eating Historia's half sister Frieda Reiss . Eren realizes by then that Rod Reiss intends to restore his family by having Historia become a Titan and eat Eren, accepting his fate out of guilt for the people he failed to save as he asks Historia to save humanity in his place . However, Eren finds Historia refusing to aid her father as she frees him as Rod becomes an Abnormal Titan while Misaka, Levi, and Jean arrive . Eren ingests a liquid labeled "Armor" that bestows him a new power to harden his Titan form, using it to save himself and his friends from being crushed by a collapsing ceiling before he and the Survey Corps head to the Orvud district where they confront and kill Rod . </P> <P> After the old regime is ousted and Historia ascends to the throne in his place, Eren and the rest of the Survey Corps depart to Shiganshina to reclaim Wall Maria by sealing its breach with his new power . However, upon arriving there, they face an army of Titans led by Zeke, the Beastly Titan, as well as Bertoldt and Reiner . The vicious battle ends with almost all members of the expedition killed, including Erwin, save for Eren and his companions, but Zeke ends up forced to flee, leaving a captured Bertoldt behind, which is later consumed by Armin to save his life . With Shiganshina secured, Eren fulfills his promise to his father by reaching the basement of their old house, where he and his friends retrieve some books and a photograph of Grisha, his first wife, Dina, who Eren recognizes as the same Titan who killed his mother, and their son, who is no other than Zeke . Upon returning home, Eren realizes that to control the power of the coordinate, he must obtain the blood of someone from the royalty, as the only moment when he managed to use it was when he got into contact with Dina, a descendant of the Eldian kings herself, in her Titan form . </P>

Who created the walls in attack on titan