The Roman ruins of Casais Velhos are the remains of a Roman town, in the civil parish of Cascais, municipality of Cascais, that included baths, two necropolis, remains of a wall and ceramic artifacts.
The villa was determined to have been constructed in the 2nd century, while traces of a wall and a turret, suggest a defensive fortification during Antiquity.
In addition to ceramic and metal artifacts, coins were also found that date between 205 and 450 A.D., suggesting a more intense occupation during the final era of the Roman empire.
The discovery of tanks and compartments with a quantity of murex shells, has led some anthropologists to assume that people in this site were involved in the dying industry (murex shells were used to produce Tyrian purple dyes). After treatment, the purple would be transported to Olisipo and from there to Rome.
The site was already known for some time, when investigators Afonso do Paço (1895–1968) and Fausto de Figueiredo began their first excavations in the structures and necropole, in the first half of the 20th century. But, apart from these first initiatives, the only new investigations began in between 1968 and 1971 (under investigators António de Castelo Branco and Octávio Reinaldo da Veiga Ferreira), whom excavated the conduit supplying the baths, as well as a reservoir and bath.
The site is located in an rural environment, situated on a hill overlooking the dunes of Guincho, in the midst of pine forests that stretch for north of the village of Areia.
The Roman villa comprises structures of that includes an upper-class domus with vestibule; a bath complex with three semi-circular baths, consisting of a frigidarium (cold baths), a warm room and transitional praefurnium (used for heating the air that circulated under the floor); and an aqueduct that supplies water to the tanks. A larger tank, possibly a Natatio was also identified.
In the upper portion of the villa, several spaces were discovered, along with two tubs with airtight lids. Two silos covered with circular slabs and carved into the rock were located, while two cemeteries (one in the eastern part of the site, while the other in the east were also discovered.
The excavation of the necropolis yielded a vast collection of ceramic vessels, jewelries, weapons and coins, the latter attributed to Constantius II(c.317-361), Constans (c.?-350), Theodosius I (c.346-395), Constantine the Great (c.271-337) and Arcadius (c.377-408), suggesting a more permanent occupation.