 Central Zimbabwe contains the "Great Dyke" – a source of serpentine rocks of many types including a hard variety locally called springstone.An early pre-colonial culture of Shona peoples settled the high plateau around 900 AD and “Great Zimbabwe”, which dates from about 1250–1450 AD, was a stone-walled town showing evidence in its archaeology of skilled stone working.The walls were made of a local granite and no mortar was used in their construction.