Megalithic monuments and extensive chambered tombs have been found at many sites in western Europe, but are often remote and peripheral: along the Atlantic coasts, the Northern Isles of Scotland and the islands of the Mediterranean. The variety is immense, comprising chambered cairns, long barrows, dolmen, cromlech, galleried graves and entrance graves – all with a plethora of sub-variants. What seems constant is the amount of labour lavished on both construction and maintenance by small communities living precarious existences. Often continuous usage is manifest for centuries or even millennia. The earliest reliably dated sites in western Europe are the Skorba temples of Malta (c. 4850 BCE). On the mainland, the Grand Dolmen of Zambujeiro in Portugal dates to c. 4000 BCE. By 2800 BCE, Stonehenge and Carnac in Brittany demonstrate a sophisticated grasp of geometry and of astronomical observation. Above all they evince a great sense of rootedness, of place, in cultures often fresh from nomadism.