Clunia (full name Colonia Clunia Sulpicia) was an ancient Roman city. Its remains are located on Alto de Castro, at more than 1000 metres above sea level, between the villages of Peñalba de Castro and Coruña del Conde, 2 km away from the latter, in the province of Burgos in Spain. It was one of the most important Roman cities of the northern half of Hispania and, from the 1st century BC, served as the capital of a conventus iuridici in the province Hispania Tarraconensis, called Conventus Cluniensis. It was located on the road that led from Caesaraugusta (Zaragoza) to Asturica Augusta (Astorga). The city declined during the 3rd century and was largely abandoned by the Visigothic era. Clunia is a toponym of Arevacian origin.

The city of Clunia was founded on a mount a short distance from a Celtiberian settlement called Cluniaco, or Kolounioukou, belonging to the Arevaci, a Pre-Roman tribe that belonged to the family of Celtiberians.

Clunia was built from scratch. Unlike other sites conquered by the Romans, Clunia did not occupy the site of an earlier city or town. Clunia boasted two public baths, a basilica, a forum, many taverns and shops, a theater, and a large temple dedicated to Jupiter.

From Livy, we know that the site was besieged by Pompey in his fight against Sertorius in 75 BC; Pompey was forced to leave Clunia partly due to weather conditions there. After resistance by Sertorius, Pompey finally destroyed what existed of Clunia in 72 BC. Clunia fell under the control of the Vacceos in 56 BC, but subsequently fell again under Roman control, as did the rebelling Vacceos and Arevaci.

Years later, the city was formally founded ex novo during the time of Emperor Tiberius, as part of the Roman plan to pacify the region after the Cantabrian Wars. It was first granted the status of municipium, and minted small coinage, asses and dupondi, on which appear the local quattuorviri, who were in charge of their minting.

The city acquired, possibly during the reign of Galba or Hadrian, the status of colonia and the epithet of Sulpicia after Sulpicius Galba, governor of Hispania, proclaimed himself emperor, and who in 68 AD took refuge in Clunia during the anti-Neronian revolution. At this town he received news of the death of the emperor and the announcement of his own elevation as emperor by the Roman Senate (because of this some essayist added the epithet of Galba to the name of the city). He traveled to Rome from Clunia.

The splendor of the Roman city of Clunia was extended during the 1st and 2nd century AD, the same as other cities of the northern plateau of Hispania such as Asturica Augusta or Iuliobriga, located in the provinces of León and Cantabria, respectively. During its maximum apogee, it is calculated that the city of Clunia came to have around 30,000 inhabitants.

During the 3rd century, a gradual depopulation of the urban nucleus took place which was connected with the crisis of the 3rd century and the incipient decline of the Western Roman Empire. It is evident that there were Barbarian invasions into Clunia. In fact, it is verified that, towards the end of the 3rd century, the city was burned by Barbarian tribes. These invasions, as well as economic instability, may have contributed to the inexorable decline of Clunia. Nevertheless, it does not appear that there was a violent and general destruction; in any event, this preludes the end of the Roman cultural influence in the city of Clunia and its surroundings. Excavations reveal destroyed urban areas in Clunia, which were not rebuilt at the end of the 3rd century. Some limited reconstruction took place during the reigns of Diocletian and Constantine, but large parts of the city were uninhabited by the 7th century, during the Visigothic era.