Halfway along the road that linked Tarraco and Asturica Augusta (Tarragona and Astorga) stood the Roman-Celtiberian city of Tritium Autrigonum (Monastery of Rodilla, Burgos). In 1986, a first photographic flight revealed the presence of urban structures, but not their architectural elements. Now the study Tritium Autrigonum: urban approach to a Hispano-Roman agglomeration based on recent aerial photographs, which will be published in full in the scientific journal Zephyrus of the University of Salamanca, reveals, for the first time, its monuments, houses, defences, necropolises and road and water supply networks. A city of approximately 45 hectares under the floor of a hill, in which Celtiberian circular dwellings from the Iron Age were surprisingly interspersed with large Roman porticoed buildings.
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This ancient Celtiberian settlement has never been the subject of archaeological excavation. However, aerial reconnaissance campaigns – carried out mainly between 2001 and 2015 – made it possible to take a large number of photographs of its surface, which is now completely covered by crop fields. The new study – authored by François Didierjean and Laurent Brassous, from the French universities of Bordeaux-Montaigne and La Rochelle – now reveals an important part of the structures buried in this urban agglomeration.
Tritium, located on the so-called Alto de Rodilla, is mentioned in Pliny's work and in the Antonine Itinerary (a kind of Michelin Guide of the time), as a city of passage between the Ebro and Duero basins. It emerged in the First Iron Age (700 BC) and lasted until about the end of Antiquity (<>th century). His complete disappearance is still an unsolved mystery.
Roman temple located at the site of Tritium.
"The site of Tritium Autrigonum," the study states, "is particularly suitable for aerial detection because it is completely devoid of buildings and is entirely occupied by fields dedicated to cereals," making buried structures more distinguishable during periods of crop maturation. The University of La Rochelle has been in charge of associating the oldest images, taken in the mid-eighties, with the most current ones (thousands of photographs), despite the difficulty of superimposing oblique photographs ―taken at different angles from light aircraft― with the zenithal ones of drones.
The constructions of Tritium that the study describes are numerous: "A square building of about 15 by 15 meters", "a large oval enclosure of 12 m long by 18 m wide", "a rectangle of 27 m long by 14 m, and with its eastern façade reinforced, probably giving it a monumental character", "a set of large premises that include a room under columns"...
But, in addition, the study reports the existence, to the north of the city, of "238 graves, between 0.60 and 3 meters in diameter, spread over approximately 7,000 square meters, which suggests a necropolis." The Romans used to open cemeteries along roads and on the outskirts of cities for health reasons.
Urban fabric of Tritium. In orange, the defensive ditches. In red, the streets. In black, the buildings. The dotted area to the south, the necropolis.P. Brunello
The aerial photographs, which have covered about 60 hectares of land, have thus uncovered "a promontory, which is almost a quadrangle, about 1,000 meters from north to south and 600 from east to west. This seems to indicate that the heart of the urbanized space was located [here], in the north, while to the south there were a few residential blocks that formed a peri-urban area. This division suggests the idea of a physical separation between the two cores, raising the question of the existence of a wall that would have divided them." Archaeologists recall that in ancient cities it is easy to distinguish between urban and peri-urban spaces, since the latter were home to cemeteries, polluting industries, warehouses and landfills.
As Tritium was fundamentally a Celtiberian oppidum, it had its own defensive system. The city was protected by steep natural slopes on its north, west and east sides, but not on the south, where surprisingly no remains of the wall have been found. This can only mean two things: either it lacked this stone defense on that side or it was destroyed at some point. The first hypothesis does not seem credible due to the importance of this oppidum built between the Ebro and Douro basins. "What could have been the defense system chosen then?" the researchers ask. "Taking into account what we know about the fortifications of the Celtiberian oppida, two possible answers can be glimpsed: either it had a wall with a moat or it was a defense formed by a set of terraces."
Tritum was, without a doubt, an important city in the Iberian Peninsula, although it was not the size of the great capitals such as Augusta Emerita or Tarraco (Mérida and Tarragona). According to experts, five monumental buildings stood out. Archaeologists believe that one of them at the top could be a temple "with two large pillars." On the southern terrace, a space of about 1,600 square meters, "with colonnades and various small structures that would be the bases of statues or inscriptions" could be the ancient forum of the city.
Roman aristocratic houses in Tritium.
They have also detected another "large quadrangular building of 1,500 square meters decorated with a colonnade on the façade and another that surrounds its interior and with several annexes." It is the characteristic floor plan of a Roman temple," they say.
In addition, they have located numerous mansions, inns and dwellings, "whose floor plans vary between a circle [between 6 and 8 meters in diameter], a square or a rectangle in very heterogeneous areas." They add: "There seems to be a mixture to varying degrees of pre-Roman traditions and influences from classical Mediterranean architecture."
The circular houses, which are mainly concentrated in the upper part of the city and on the northern periphery, had a central post that supported the roof, a type of construction characteristic of the First Iron Age. "Were these houses still functioning in Roman times?" the archaeologists ask again. "Its traces are faint, and there are several cases of overlap with quadrangular [Roman] structures, which were probably built later. In Tritium, the distribution of circular dwellings, mainly on the northern periphery, could indicate the survival of ancient forms of habitat for low-income populations. If this is not the case, the settlement of the First Iron Age must have had considerable importance."
The Roman houses detected, on the other hand, were "relatively large buildings, organized around a central courtyard, two of them with colonnades, and equipped with rooms with floors, probably of masonry, which could attest to the presence of mosaic floors or hypocausts [underfloor heating system]."
Experts believe that "the indigenous structures of the summit were preserved during the establishment of Roman domination. After the conquest, buildings inspired by the classical tradition were not erected in the highest part of the city, but on its nearby periphery. This arrangement is not exceptional in the Romanized cities of the Iberian Peninsula, especially on the east coast and in the Ebro valley. However, confirmation of this hypothesis can only be obtained through archaeological excavations that provide the chronological data necessary to date the occupation of the different spaces."
Given the importance of this city – it was next to the road that linked Tarraco and the gold mines of the northwest – "it is worth asking why and when it was abandoned". These questions can only be answered with further studies and archaeological excavations at the site, but their application provokes the rejection of some landowners. "Hopefully it's only temporary," the French researchers conclude.
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