Almendres Cromlech , Portugal , 4000 B.C.

The Cromlech of the Almendres megalithic complex (or Almendres Cromlech), located near Guadalupe, in the civil parish of Nossa Senhora de Guadalupe, municipality of Évora, is the largest existing group of structured menhirs in the Iberian Peninsula, and one of the largest in Europe.The construction of these structures date back to 3000 B.C., or to as early as 4000 B.C., and only rediscovered in 1966 by Henrique Leonor Pina who was preceeding in field work assocaited with the geological charts of the country.
-Wikipedia-