On our way north from Nazaré to Porto we stopped at the site of a Roman settlement in Portugal, known as Conimbriga, which is about halfway between those two cities (roughly 110 km or 68 miles either way). The history of Conimbriga actually dates back well before the Romans, to the Bronze and Iron ages. It was an ideal location, on a plateau that was easy to defend and good access to water.
What remains are the Roman-era ruins, of which 17% have been excavated, leaving a lot more to discover. The visible ruins date from about mid 1st century CE to about 500 CE, when the Roman empire finally completely collapsed. Although most of the structures are pretty ruined, enough remains to get a feel for the wealth and prosperity of Conimbriga in its prime.
The largest aristocratic residence, known as the House of Fountains, sits just outside the walls. It was constructed around 200 CE and excavated in 1939. It has a huge courtyard (or peristyle) with pools, fountains and beautiful mosaic floors in its rooms. Unfortunately, it was largely demolished when the defenses of the town were strengthened and building material was needed. The remnants of this 35,000 sq. feet residence are still interesting, protected by an overhead shelter.
There are remains of other buildings inside the city walls, including a forum, basilica, and other dwellings. The Romans were amazing engineers and builders, their ability to construct a city layout with infrastructure that is still partially intact today speaks to their skills.
In addition to the ruins at Conimbriga, there is a small museum on the site, and there are a few other small Roman ruins north and south (Alcabideque, Rabaçal and Santiago Da Guardia), indicating the expanse of Roman civilization in this part of Portugal.