Juliobriga was the most important urban centre in Roman Cantabria, as stated by numerous Latin authors including Pliny the Elder. The site has traditionally been identified with ruins in the village of Retortillo in the municipality of Campoo de Enmedio.
Its founding, during the Cantabrian Wars (29 BC-19 BC), made it a powerful symbol of Roman domination of the tribes of the Cantabri. The city was named after the reigning emperor Augustus and his adopted family name, the gens Julia, with the Celtic toponym element -briga, common in Iberia. Due to its strategic location in the Besaya valley, it was able to control trade between the Douro river and the Bay of Biscay. Juliobriga grew slowly, reaching its peak between the end of the 1st century and the early 2nd century AD. Following that, its population began to decline, until the city was completely abandoned in the 3rd century.
The ruins of Retortillo were first identified with Julióbriga in the second half of the 18th century by Enrique Florez. Numerous historians and archaeologists have worked on the site since, including some of Spain's foremost.
References:The ancient Argos Theater was built in 320 BC. and is located in Argos, Greece against Larissa Hill. Nearby from this site is Agora, Roman Odeon, and the Baths of Argos. The theater is one of the largest architectural developments in Greece and was renovated in ca 120 AD.
The Hellenistic theater at Argos is cut into the hillside of the Larisa, with 90 steps up a steep incline, forming a narrow rectilinear cavea. Among the largest theaters in Greece, it held about 20,000 spectators and is divided by two landings into three horizontal sections. Staircases further divide the cavea into four cunei, corresponding to the tribes of Argos A high wall was erected to prevent unauthorized access into the theatron and may have helped the acoustics, but it is said the sound quality is still very good today.
Around 120 CE, both theaters were renovated in the Roman style.