Paradis Island is a massive Eldian island on which the Walls Rose, Sina, and Maria are located. It is just off the coast of Marley and is sorrounded by the sea. Marley uses the island as a dumping ground for its Eldian criminals, turning them into Pure Titans as punishment. In this context, the island is often called "paradise".
By the year 851, the island has been cleared of Pure Titans thanks to the use of the Executioner from Hell devices, allowing its inhabitants to roam freely outside the Walls.
Following Eren Jaeger's initiation of the Rumbling, civilization advances on the island for many years before it is eventually destroyed by war.
History: Late into the history of the Eldian Empire, Karl Fritz, the 145th monarch of the Fritz family, chose to abandon the conflict over the Nine Titans between the subservient Eldian families on the continental mainland. Karl, ashamed of Eldia and its history of persecuting Marley conspired with the Tybur family to ensure Marley would win the conflict and overthrow the Empire and moved the capital of Eldia to Paradis Island, a remote island at the time. In the King's absence, the Great Titan War crippled the Eldian Empire as the eight Titan families would engage in an endless cycle of conspiracy and betrayal, which allowed the oppressed Marleyans to rise up.
Story: Marley sends members of the Warriors: Reiner Braun, Bertholdt Hoover, Annie Leonhart, Marcel Galliard to retake the Founding Titan. Marcel is eaten by a Pure Titan while the other 3 make their way to Wall Maria. An abnormal Titan enters the city, finding and eating Grisha's wife Carla in front of Eren and Mikasa.
Trivia: " If mirrored vertically, the continent controlled by Marley and the island of Paradis are very similar to the real-life continent of and the island of , respectively.
Source: Paradis Island (Anime), available under CC BY-SA 3.0.