The Fall of Wall Maria (ウォール・マリア陥落 Wōru Maria kanraku?) was a tragic disaster which began when Shiganshina Distict came under the attack of the Colossal 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.
On the morning before the fall, Commander Keith Sadies returned to Shiganshina District from an expedition beyond Wall Maria with devastating losses. With the Scout Regiment's drastically reduced numbers, the people of the Walls were all the more susceptible to the Titans.
Elsewhere in Shiganshina, Grisha Jaeger made plans to travel to the interior on an appointment. Before leaving his home, he promised his son Eren Jaeger that upon his return, he would show him the secret he had kept secret in the cellar of their home.
In the afternoon following the return of the defeated Scout Regiment, the attack on the Walls began when the Colossal Titan appeared beyond the south gate of Shiganshina District, breaking the gate apart and breaching Wall Maria in a single kick. Presumably at this time, Annie Leonhart used the Female Titan to attract countless Titans to the breach where they would invade humanity's territory. As Titans began to enter the district, the civilians started to evacuate in a horrified panic while the Garrison set up a hasty defense.
During the massacre, Eren Jaeger and Mikasa Ackermann 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 Garrison soldier Hannes, a family friend, rushed to their aid. Confident he could slay an incoming Titan, Hannes rushed into action hoping to save the entire family, but soon found himself unable to face the Titan. Unnerved and losing the will to fight, Hannes saved Eren and Mikasa and evacuated with them as Carla, accepting her fate, was eaten by the Titan as Eren watched.
Unable to contain the invading Titans, the Garrison evacuated any survivors they could to the gate and packed them into ferries that would transport them to Wall Rose. A small group of soldiers under the command of Hugo assigned cannons to defend the gate, trying to hold off the advancing Titans. Hannes argued against closing the gate, which would stop the advance of the Titans but also doom the civilians who had not yet evacuated. Before a conclusion could be made, the Armored Titan charged the north gate of Shiganshina, with Garrison cannonfire proving useless against him. The Armored Titan succeeded in breaching the north gate, and with that Wall Maria was fallen.
Shortly afterwards, Grisha reunited with his son. He urged Eren to return to Shiganshina in the future in order to discover the secrets within the cellar of their home. He injected Eren with a strange serum, and Eren forgot the events that followed. However, after that moment, Eren mysteriously possessed the ability to transform into a Titan.
With an abundance of refugees coming into Wall Rose's territory, humanity faced a severe food crisis. Refugees were tasked with working the farmlands of Wall Rose to alleviate the impending shortages. In order to alleviate the food shortages, the central government made plans to announce an operation to reclaim Wall Maria. While the operation's public purpose would be to reclaim humanity's lost territory, its true purpose would be to thin the human population so that the surviving residents of Walls Rose and Sina would not be at a loss for necessary food and supplies.