Attack on titan series: It's an adaptation of the manga series created by Japanese illustrator Hajime Isayama. Three seasons have been aired until now with the forth coming this fall. The story takes place in an apocalyptic world where the last surrvivors of humanity are forced to live in a city surrounded by enormous walls (50 meters)that portect them from gigantic man-eating monsters known as Titans.Three walls surround the city : The outter wall called Maria The middle wall called Rose The innermost wall called Sina With the distance between wall Maria and rose being 100KM,Rose and Sina being 130KM. The humanity was living 100 years in peace until a titan(Colossal Titan) taller than the wall (60 meters)cracked open wall Maria's gate allowing smaller titans (Pure Titans) breach the wall. The story focuses around a young boy called Eren Yeger who vows to kill all the titans and retake his hometown and avenge his mother's death.