This UNESCO cover from Portugal depicts a stamp issued in 2018 celebrating the "Prehistoric Rock Art Sites in the Coa Valley", an open-air Paleolithic archaeological site located in northeastern Portugal, near the border with Spain. In the early 1990s rock engravings were discovered in Vila Nova de Foz Côa during the construction of a dam in the Côa River valley. They include thousands of engraved rock drawings of horses, bovines and other animals, human and abstract figures, dated from 22,000 to 10,000 years B.C. The Prehistoric Rock-Art Sites in the Côa Valley were designated a World Heritage Site by UNESCO in 1998. The archaelogical site of Siega Verde, province of Salamca, Spain, was also added to the Côa Valley Paleolithic Art site in the World Heritage List in 2010.
