Leviathan of Dis

From Mass Effect Wiki

The 'Leviathan of Dis' is the name given to a gigantic corpse discovered in a crater on Jartar in 2163. It is believed to be the remains of a genetically engineered starship and its age was originally placed at nearly a billion years old.

However there was little time to study it. Not long after its discovery by a batarian survey team, a batarian dreadnought visited the Dis system, after which the Leviathan mysteriously disappeared. The batarians have since strenuously denied that the Leviathan existed at all. They become even more vocal when showed documentation of the Leviathan by salarian researchers before its disappearance.