Walls (Anime)

The Walls (壁) are large structures that surround the remaining territory that humanity inhabits. They were built more than a century ago and contain skinless Titans inside their hollow shell.

Description
The Walls reach about 50 meters in height from base to summit and are incredibly strong in substance. However, the Female Titan was able to damage them when she attempted to climb over it.

The Walls are too long to be guarded in their entirety. The tops of the Walls are lined with cannons, which can fire on approaching Titans, even though they are not particularly effective due to the Titan's regeneration abilities. To account for this, each one has four towns on their periphery known as "districts". As Titans are drawn towards large concentrations of people, humanity can focus its defenses at these districts and not the rest of the Wall. The districts are considered the worst and least desirable places to live, as they are at greater risk of a Titan invasion.

Few people know about the Titans within the Walls. The Scout Regiment learned of their existence when the Female Titan damaged the surface of Wall Sina, exposing the face of a huge Titan. Minister Nick, a foremost member of a cult which considers the Walls to be holy, knew of the Titans within them, but would reveal no more under the interrogation of Hange Zoë. It is unknown how commonplace this knowledge is within the Church of the Walls.

History
One hundred and seven years ago, it is said that humans were brought to the brink of extinction at the hands of the Titans "almost overnight". In response to this, the survivors made huge Walls to protect their last stronghold.

The current status of the Walls is chaotic. Shiganshina District was the first city to fall when Wall Maria was breached, leading to a massive slaughter and prompting humanity to abandon the entire perimeter and the remaining cities along the Wall as they attempted to consolidate their losses. After the fall of Wall Maria, humanity was pushed into Wall Rose. Soon after a massive campaign to retake Wall Maria was launched as nearly 250,000 conscripted soldiers were sent out to wipe out the Titans; this campaign ended in disaster and saw the near-total annihilation of the army tasked with this mission. Within five years after that, Trost District was breached, though it ultimately survived due to the intervention of Eren Jaeger, while also ensuring the local population's survival. Some time later, Wall Sheena and Stohess District were heavily damaged when Eren did battle with the Female Titan. On the same day, multiple Titans were spotted inside Wall Rose coming from the south.

The Science of Attack on Titan
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 Colossus 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. It is unknown whether the King's claim was accurate to the Wall Titans' numbers or was hyperbole.

Trivia

 * Titans primarily targeted the southern region, even before the loss of Wall Maria. As such, they are considered the most dangerous and least desirable places to live in.
 * The northern districts are considered the most desirable region, due to minimal Titan activity. However, the weather is brutally cold and makes life for residents very difficult. Hajime Isayama suggested they may have hot springs to make up for the harsh weather.
 * Isayama has described the northern region as relatively cold, rarely exceeding even on the hottest summer days.
 * "Rose" was the East Germany's secret codename plan to build the Berlin Wall.
 * In the early draft of chapter 1 presented by Isayama to the editors of the, Wall Maria and Wall Rose were switched, so Wall Rose was the outermost Wall breached by the Colossal Titan, and Wall Maria was the second outermost Wall to where the survivors retreated.