Atlantinopolis is a city on the planet Moebius, located on the Sunken Island. It is an alternate version of Echidnaopolis, but is believed to be uninhabited except for Overseer O'Nux and the Orderix. It was threatened with destruction by Dr. Robotnik and Evil Sonic when they tried to steal its Anarchy Beryl, but thanks to the Knothole Freedom Fighters and Knuckles Prime the city was saved. It was presumably either conquered or destroyed by Scourge the Hedgehog when he battled Anti-Knuckles. (StH: #44, #193, CSE)
- The city's name is based on Atlantis, a mythical city believed to have disappeared into the sea.