This period was characterized by exploitation of the ecosystem in the Sado Estuary, when the river extended to São Romão, involving fishing, scavenging for shellfish, hunting and foraging in the local forests.

Mediterranean trade, pioneered by the Phoenicians, introduced commercial colonies in Abul and Alcácer (then referred to as Bevipo or Keition), where a written alphabet and currency allowed commerce to flourish.

Returning to the Imperial fold with the 296AD reorganization of Roman territories by Diocletian (in order to subvert the Military Anarchy that existed at the time), Salatia's role was transformed.

The Ummayad rule on the Iberian Peninsula, in the reign of Abu-l-Khattar (743-745) over the region of Beja, which included Alcácer, was noted for the recruitment of troops, and for the rising power of Yemeni clans in southern Portugal.

[6] In 997 a Moorish fleet transported troops from Alcácer to Porto, to support Al-Mansur Ibn Abi Aamir, that culminated in the destruction of the sanctuary of Santiago de Compostela.

[9] According to De itinere Frisonum the Frisian Crusaders refused to help on account of Innocent III prohibition to Bishop Souiro, and departed for the Holy Land, even after being provided food, expenses, and rousing oratories about the Almohads' annual demands for 100 Christians in tribute.

[12][13] Once the castle was taken, many of the northern Crusaders requested Pope Honorius III allow them to remain for a year "for the liberation of Hispania" and "the extirpation of the perfidious cult of the pagans".

[9] The victory in Alcácer do Sal also motivated Alfonso IX of León, Sancho VII of Navarre, in addition to Iberian prelates and nobles, to break their truces with the Muslim leaders, in hopes that the northern Crusaders would continue their campaigns the following summer.

[7] Along with the Christians and the town's small population of Jews, the remaining Muslims in Alcácer do Sal begin to occupy the low country along the river, and vacate the Castle.

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.

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.

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.