Mértola is a town and municipality in southeastern Portuguese Alentejo near the Spanish border. In 2011, the population was 7,274, in an area of approximately 1,292.87 square kilometres (499.18 sq mi): it is the sixth-largest municipality in Portugal. Meanwhile, it is the second-lowest population centre by density with approximately 5.62 persons/1 square kilometre (0.39 sq mi).