Juliobriga (Spanish: Julióbriga, (Latin: Iuliobriga, Ancient Greek: Ἰουλιὃβριγα) 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 (Cantabria) and its Villafría district, 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. The ruins of Juliobriga were declared a Heritage Site (Spanish: Bien de Interés Cultural) by the Spanish Government on March 29, 1985.
- "But among the seven peoples belonging to the Cantabri, Juliobriga is the only place worthy of mention" Pliny the Elder, Natural Histories III.4.27
- The ruins are 4km (2.5 mi) southeast of Reinosa near the reservoir of the river Ebro.((in Spanish) Iglesias Gil, JM. Julióbriga, p. 5.)
- (in Spanish) Mangas Manjarrés, J. La Hispania Romana. en Manuel Prado, J. (dir.) Historia de España. Esplugues de Llobregat: Ediciones Orbis, S.A.; 1991. Vol. I «Prehistoria a 409», p. 192. ISBN 84-01-61513-5.
- "The same Indo-European root is also the origin of the Germanic cognates berg or burg, Gothic baurgs. The first meaning is, apparently, something like 'hill', from whence comes 'fortress' or 'fortified town', until we may eventually get simply to the idea of an urban enclave that was not necessarily fortified." (Juan Luis García Alonso, "-Briga Toponyms in the Iberian Peninsula" e-Keltoi 6).