Sophisticated civilization in El Salvador dates to its settlement by the indigenous Lenca people; theirs was the first and the oldest indigenous civilization to settle in there. They were a union of Central American tribes that oversaw most of the isthmus from southern Guatemala to northern Panama, which they called Managuara. The Lenca of eastern El Salvador trace their origins to specific caves with ancient pictographs dating back to at least 600 AD and some sources say as far back as 7000 BC. There was also a presence of Olmecs, although their role is unclear. Their influence remains recorded in the form of stone monuments and artefacts preserved in western El Salvador, as well as the national museum. A Mayan population settled there in the Formative period, but their numbers were greatly diminished when the Ilopango supervolcano eruption caused a massive exodus.