Mértola () is a municipality in southeastern Portuguese Alentejo near the Spanish border. In 2011, the population was 7,274, in an area of approximately : it is the sixth-largest municipality in Portugal. Meanwhile, it is the second-lowest population centre by density with approximately 5.62 persons/ (second to the adjacent Alcoutim). The seat of the municipality is the town of Mértola, which has around 2800 inhabitants (2011), located on a hill over the Guadiana River. Its strategic location made it an important fluvial commercial port in Classical Antiquity, through the period of Umayyad conquest of Hispania: Mértola's main church (the Church of Nossa Senhora da Anunciação) was the only medieval mosque to have survived the period in Portugal. In 2017 Mértola started the process to become a UNESCO World Heritage Site. History Romans Mértola was inhabited at least since the Iron Age at least by Conni and Cynetes settlements, was influenced by the Phoenicians and finally named Myrtilis Iulia by the Romans. The strategic location of Mértola, on a hill by the northernmost navigable part of the Guadiana river, was crucial in its early development. Agricultural products grown in the villae nearby and valuable minerals (silver, gold and tin) obtained from the lower Alentejo region were sent from the fluvial port of Mértola via the Guadiana to Southern Hispania and the Mediterranean. Between 1st and 2nd century, Myrtilis, was part of the larger Pacensis region (under the capital Beja/Pax Julia), acquired a great importance, as a dynamic commercial centre, permitting it to mint its own coin. The town was raised to the status of a Municipium in times of Emperor Augustus and was connected to important Roman cities (Beja, Évora) through a road system. Germanic tribes During the Migration Period, Mértola was invaded by Germanic tribes of the Sueves and the Visigoths. In this period (5th-8th centuries) commerce was reduced but still active, as evidenced by Greek tombstones from the 6th-7th centuries found in Mértola which suggest the presence of Byzantine merchants in the town. Moors Around the year 711, Hispania was invaded by the Moors from the Maghreb, inaugurating a period of great influence of Islamic culture in the Alentejo region that would last over 400 years. Mértola and its port played an important economic role in the commerce of agricultural and mineral goods between the Alentejo and other parts of Al-Andalus and Northern Africa. Mértola had a wall dating