The Walls exist since more than a century ago. The humans started to become extinct at the hand of the Titans. Due to this the humans made huge walls to protect their last stronghold. The walls reach about 50 metres in height. The tops of the walls are lined with cannons, which can fire on approaching Titans.
Because the walls are too long for humanity to guard their entire lengths, each has four towns on their edges. Because Titans are drawn towards large concentrations of people, they focus their attacks on these towns, and humanity's defenses can be focused there.
The interior of the walls seem to contain numerous dormant Titans. However no details have been given, it has been suggested that the walls were originally created by Titans using their hardening ability.
Two of the few people who know about the Titans in the walls are Pastor Nick and Historia Renz. Pastor Nick is a foremost member of a cult which considers the walls to be holy. Historia was a formerly high-born lady and presumably knows about the walls because of that.
|Wall Maria is the outermost wall of the human kingdom. Like the other walls, Wall Maria is approximately 50 meters in height. Five years ago, it was breached by the Colossal Titan after about 100 years of peace and prosperity.|
|Wall Rose is the second outermost wall following Wall Maria. It has been breached by the Colossal Titan after 5 years of the Wall Maria being breached, but has been covered by a boulder with the help of Eren Jaeger. It was thought to have been breached again after Titans appeared inside it.|
|Wall Sina is the innermost wall protecting the kingdom where the king and other civilians reside. The city inside Wall Sina is protected by the Military Police serving under the king.|