Fall of Wall Maria

The Wōru Maria kanraku (ウォール・マリア陥落) was a tragic disaster which began when Shiganshina District came under the attack of the Colossus and Armored Titans, in which humanity was forced to retreat to Wall Rose as the Titans entered humanity's territory for the first time in a hundred years.

Prelude
Around twenty years ago, the nation of Marley began to consider the necessity of claiming the immense amount of fossil fuels on the island of Paradis where the majority of the remnants of the nation of Eldia lived within the three Walls Maria, Rose, and Sheena. Over eighty years ago, King Fritz had issued an ultimatum to the nation of Marley at the end of the Great Titan War: if Marley made any move of hostility against the Eldians of Paradis, the King would use the Progenitor Titan to release the countless Colossus Titans contained within the Walls. In order to claim Paradis without a direct act of war, the Marleyans chose to begin a warrior program. In this program, low-class Eldian citizens within Marley would offer their children between the ages of 5 and 7 to the Marleyan military, where they would train until seven would be chosen to inherit the seven Titans in Marleyan possession, obtained during the Great Titan War.

Fifteen years later, four Eldian warriors were chosen to be sent out of their "Hometown" to begin the attack on Paradis: Bertolt Hoover, Reiner Braun, Annie Leonhart, and Marcel.

Shiganshina District
After nearly a century of undisturbed peace, the humans of Shiganshina had become content in their confinement and thought little of the Titans who had been vainly clawing at their doorstop for decades. As such, they thought little of the sacrifices of the Survey Corps who had continued to make ultimately futile efforts to eliminate the Titan presence beyond the Wall, coming back to once again concede that the deaths of their comrades had all been for nothing. The soldiers of the Garrison had become undisciplined and disdainful of their posts, and thus were completely unprepared for the holocaust that was to come.

Finally, in 845, the peace was abruptly ended when the Colossus Titan suddenly appeared at the gates of Shiganshina, much to the horror of the thousands of citizens and soldiers trapped within. The Colossal Titan then proceeded to smash its foot through the outer wall, sending a shower of debris raining across the city and killing dozens of panicked civilians as dozens of mindless Titans began pouring in from the outside. The city descended into chaos as the Titans began to devour the humans by the hundreds, and the Garrison scrambled to evacuate the survivors to the inner wall as they found themselves hopelessly outmatched by the Titans.

During the massacre, Eren Yeager and Mikasa Ackerman rushed back to their home to find that their mother Carla was trapped in the debris and unable to move, and the two children desperately tried to free her without success. Carla pleaded them to save themselves when the soldier Hannes rushed to their aid. Confident he could slay the incoming Titan, Hannes rushed into action hoping to save the entire family, but soon found himself facing the Smiling Titan. Unnerved and losing the will to fight, Hannes raced back to save Eren and Mikasa, against the former's protests even as Carla pleaded them to let her be and to get to safety. Hannes dragged the children away from the house as the Smiling Titan plucked Carla from the wreckage, violently broke her back, and then proceeded to devour her lifeless body, with her son only able to look back in horror.

Unable to contain the invading the Titans, the Garrison evacuated any survivors they could to the gate and packed them into ferries that would take them deeper inside humanity's territory. The situation soon fell completely out of control as thousands fought to escape the city. A small group of soldiers under the command of Hugo assigned cannons to defend the gate, trying to hold off the advancing Titans who largely ignored their fire. As the last ferry was loaded, a completely new breed of Titan covered in armor-like skin appeared, and began charging at the inner wall at top speed. Unable to take it down with cannon fire, the Garrison soldiers panicked and fled for the closing gate, but the Armored Titan then smashed its way through, killing many of the Garrison soldiers and civilians still gathered at the entrance. The final ferry pulled away packed with survivors, leaving hundreds more behind who had been unable to board. The Titans slowly exterminated the doomed population of Shiganshina and then continued into human territory, signaling the fall of Wall Maria.