1482, when they returned to Palmela. Along with the Christians and the town's small population of Jews, the remaining Muslims in Alácer do Sal begin to occupy the low country along the river, and vacate the Castle. The Muslims, under the "King's protection" remained in the community. In 1495, Manuel I was acclaimed King by the residents of the village. Slave trade By the 16th century, the whole Sado Basin, where Alcácer do Sal is located, had experienced an important African immigration as a way to compensate for the demographic deficit that accompanied the Portuguese overseas expansion. Later, in the 18th century, a new wave of slaves was recruited to Alcácer do Sal to work the salt fields and cultivate rice, the two important economic activities in the region. A recent genetic study in 2010 found in Alcacer the highest frequencies (22%) of Sub-Saharan maternal lineages reported so far in Europe and, according to the authors, likely associated with the influx of African slaves between the 15th and 19th centuries. Geography Physical geography A few kilometres from the city of Alcácer, along the course of the Sado, is the Reserva Natural do Estuário do Sado (Sado Estuary Nature Reserve) which covers an area of , comprising marshes, canals, streams and mangroves. Human geography The municipality is bounded to the north by the municipalities of Palmela, Vendas Novas and Montemor-o-Novo; northeast by Viana do Alentejo; east by Alvito; south by Ferreira do Alentejo and Grândola; to the west, also by Grândola, along a branch of the Sado Estuary; and northwest by the Setúbal. Alcácer do Sal is a historical city and municipality that overlooks the Sado River; its medieval town developed from barrios that surrounded an ancient Muslim castle. Alcácer do Sal is the municipal seat, which includes two civil parishes, both having a population of 6002 residents. The second-largest municipality () in the country, it is administratively subdivided into four civil parishes (): Alcácer do Sal (Santa Maria do Castelo e Santiago) e Santa Susana Comporta - part of the larger Comporta Coast region; although a traditional a centre of rice cultivation and fishing, the parish and villages have seen more interest recently with luxury tourism, associated with the white-sand beaches of the Sado estuary, and its proximity to the coastal beaches of the Atlantic. Its resident population is less than 1400 permanent inhabitants, although throughout the summer these numbers