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: 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. The seat of the municipality is the town of Mértola, which has around 2800 inhabitants, located on a hill over the Guadiana River.