In the western margin of the Guadiana river, overlooking the salt marshes, is the castle of Roman foundations, which was enlarged in the medieval period and became the headquarters of the 'Order of Christ' Knights, religious military order which had succeeded the 'Templars' of Portugal. In the XVII century, was built a fort (Fort São Sebastião) of defensive nature against Spanish attempts of incursion in Portuguese lands.

The area surrounding the Castro Marim is currently classified as 'Nature Reserve' due to the numerous birds that nest in these marshes areas.

The wetland fostered the creation of saline as a economic propellant in parallel with its safe harbor for ships that sailed up the river Guadiana in trade of metals, specifically copper and gold that was mined up river, in places like Alcoutim and Mértola in Alentejo.

All the success of Castro Marim left deep cultural marks that contrast with the current reality. Castro Marim has an aging population since the county's economic stimulus died and little or nothing has been done to find it again.

It is of note that the Guadiana International Bridge, which allows traffic between Portugal and Spain, brought little or nothing to the local economy.

Castro Marim stopped in time, making it an excellent tourist destination.