Orcus Patera is an enigmatic elliptical depression located between the volcanoes of Elysium Mons and Olympus Mons. This well-defined depression extends approximately 380 by 140 kilometres in a north-northeast to south-southwest direction. It has a rim that rises up to 1800 metres above the surrounding plains, while the floor of the depression lies 400 to 600 metres below the surroundings. The term 'patera' is used for deep, complex or irregularly shaped volcanic craters such as the Hadriaca Patera and Tyrrhena Patera at the north-eastern margin of the Hellas impact basin. However, despite its name and the fact that it is positioned near volcanoes, the actual origin of Orcus Patera remains unclear.