The Gallo-Roman enclosure of Tours is a wall surrounding the city of Civitas Turonorum (the cathedral quarter of the current city of Tours) and was constructed during the Late Roman Empire. It is commonly referred to as the "castrum enclosure." Only the remaining Gallo-Roman construction in Tours is accessible to the public. The enclosure has been designated a historical monument since 1927.
The structure was erected in the early years of the 4th century in the northeastern sector of the open city that had been established during the High Empire era. This construction was undertaken in response to the prevailing insecurity experienced in Gaul during this period. Many other cities subsequently adopted similar defensive measures. However, the implementation of this particular structure was not carried out hastily. This enclosure, which had a perimeter of 1,245 meters, was constructed using recycled materials sourced from existing buildings. The structure was supported by the amphitheater of Tours, which was converted into a monumental gate in the south of the new city. Approximately fifteen towers reinforced it, and several gates and posterns pierced it. The Loire River bathed its northern wall. When Tours expanded and built new enclosures in the 12th century and two centuries later, the castrum wall served as the base for the eastern part of the new constructions.
The meticulous archaeological excavations conducted from 1974 to 1978 on the site of the Tours castle (referred to as "site 3" by archaeologists) were followed by exhaustive studies in the early 1980s. These studies were completed at the end of the 20th century and the beginning of the 21st century, providing a comprehensive understanding of the architectural features of the site. However, considerable uncertainty persists regarding the structuring of space within the Cité, the nine hectares enclosed by the enclosure, and the number and social characteristics of its residents. A hypothesis is emerging that sees the northern half of the space inhabited by "civilians", including representatives of the administrative authority, while the southern half was reserved for religious individuals around the episcopal pole. It seems reasonable to posit that the city of Tours of the Late Empire did not confine itself to this fortified enclosure. However, the organization of the space outside the walls remains shrouded in obscurity.
Geographical and historical context
Local constraints At the beginning of the 3rd century, the city of Tours, founded in the first half of the 1st century AD, had already undergone significant changes. Like two-thirds of the cities in northern Gaul,: D'Auguste au vie siècle : transformation dans le réseau des cités it gradually replaced its Latin name with that of its people, abandoning Caesarodunum for Civitas Turonorum. The urban fabric appears to have gradually retreated from the city's periphery towards the Loire front, which was less susceptible to flooding and where the most densely populated area was already concentrated. This modification of the urban envelope seems to be accompanied by a profound change in construction methods: In the elevation of the walls, masonry is replaced by wood and earth, which does not contribute to the preservation of remains and may partly explain the lack of archaeological information from this period.: Préambule historique et archéologique
The reasons for this evolution, which was observed in most Roman cities in Gaul during Late antiquity, are not precisely known but are undoubtedly multiple. The Crisis of the Third Century of the Roman Empire led to a decline in economic activity and disrupted the functioning of the administration. Local factors may also have played a role; it is likely that floods of the Loire, like those experienced by Tours at that time, contributed to this modification of the urbanized area. Furthermore, Tours faced the problems of insecurity related to barbarian incursions, which began in 250 and invaded the northern provinces of Gaul from the Germanic limes.: Duby, Invasions du iiie siècle; trésors monétaires et incendies
Consequently, the inhabitants were compelled to confront the novel circumstances of a city vulnerable to assaults, even as its infrastructure was gradually disintegrating or, at the very least, undergoing a radical transformation. In the second half of the 3rd century, the inhabitants began fortifying the amphitheater and surrounding it with a ditch.: Les trois temps de l'amphithéâtre antique They then considered constructing an enclosure with a tightened perimeter that would house the administrative authorities of the city, serve as a refuge for the inhabitants in case of attack, and ultimately consecrate the birth of a new city from an urbanistic point of view.: La fortification de la ville au ive siècle : un nouveau plan d'urbanisme
Dating of the enclosure Evolution of dating hypotheses for the castrum.
(1776): under Julius Caesar. (1828): around 474–475. (1831): early 5th century. Charles de Grandmaison (1859): between 250 and 300. Émile Mabille (1862): 373–385. Robert Ranjard (1958): early 4th century.: L'histoire de Tours Henri Galinié and (1981): 370–380.: Le rempart du castrum (2007): completion around 350.: La fortification de la ville au Bas-Empire, de l'amphithéâtre forteresse au castrum After formulating numerous hypotheses regarding the dating of the castrum, archaeologists and historians have reached a consensus that the structure was constructed for several years, or even two or three decades, in the first half of the 4th century.: L'enceinte gallo-romaine This dating is corroborated by the construction techniques typical of this period, including the use of opus mixtum,: L'histoire de Tours the resumption of activity around 370 of the High Empire baths located in its northwestern corner after their redevelopment following the construction of the enclosure, and finally by the abandonment of a defensive ditch previously built on the same site and revealed on part of the perimeter of the amphitheater.: La date du rempart: L'enceinte gallo-romaine
Subsequently, between 364 and 388, Tours benefited from an administrative reorganization of the Roman Empire and was elevated to the rank of capital of the Third Lyonnaise.: La civitas Turonorum au iiie et au ive siècleThe IIIe Lyonnaise included Touraine, Anjou, Maine, and Brittany. This period also saw the development of Christianity, notably under the episcopate of Martin. In 1979, Henri Galinié and Bernard Randoin proposed that the construction of the castrum may have been the cause or consequence of Tours' accession to the rank of provincial capital of the Roman province.: Tours au Bas-Empire However, if the first proposition cannot be affirmed or denied, the second is no longer acceptable, as the chronology now establishes the precedence of the urban plan modification over the status change.
The wall would be reused, except its western flank, in several successive enclosures of Tours. These include the extension of the Arcis enclosure from the 12th century (listed in the General inventory of cultural heritage in 1991) and the 14th-century enclosure (listed in the General Inventory of Cultural Heritage in 1991), called Clouaison de Jean le Bon.By letters patent dated March 1356, King John II "the Good" authorized the inhabitants of Tours to continue the construction of a new enclosure intended to unite the various urban nuclei that would constitute the late medieval city (). This continued use is responsible for the survival of the GalloRoman enclosure of Tours, despite significant modifications and restoration efforts.
Architecture
The enclosure in the Late Empire
Origin of materials
The construction of the enclosure employed a systematic recycling of materials, using large blocks, small retouched stones, and tiles. These materials were sourced from monuments and buildings situated outside the enclosure perimeter. The large blocks, capitals, frieze blocks, and columns were likely obtained from public monuments within the city. The total mass of large blocks used in the wall construction is estimated at 50,000 tons.: Genèse du paysage urbain The small stones and terracotta (tubuli,Tubuli were terracotta pipes that channel hot air or smoke in ancient baths. brick, or tile fragments) are believed to have originated from private houses situated close to the rampart.: Le rempart du castrum Several funerary elements (stelae) discovered in the foundations provide clear evidence of borrowings from the necropolises of Caesarodunum.: Deux nécropoles aux portes de la ville The contributions of reused materials may even have a more distant geographical origin. During his visit to Tours, Emperor Constantine requested that the stones from Amboise, a city located 25 km from Tours, be used for the construction of the rampart.: Tours au Bas-Empire This massive reuse of old building materials is not an isolated case and does not imply an accidental abandonment of old buildings. Rather, it was common in the Roman Empire to program the recycling of old materials in new constructions.: Les enceintes urbaines
Foundations The precise structure of the monument remains unknown, as no excavation has yet reached its base.: L'architecture de l'enceinte urbaine du ive siècle The structure is composed of several courses of large recycled limestone blocks, including hard chalk or tuffeau stone, raw or sculpted blocks, capitals, column drums cut in half, and other materials. These blocks are stacked with tight joints in a trench at least 3 meters deep, with a width that far exceeds that of the wall in elevation. The upper level does not exceed that of the ancient ground, around 48.50 meters NGF. The ancient ground, at approximately 48.50 meters NGF, appears to be relatively consistent throughout the entire perimeter of the enclosure. At least six courses of large blocks have been identified on site 3, and it is not excluded that the base of the foundations, at least in this sector along the Loire, is established on wooden piles.: Le mur de l'enceinte urbaine du ive siècle. Étude architecturale While the exterior side of the foundations is aligned with the alignment of the wall of the enclosure, the interior side extends approximately 1.50 meters in the northwest corner, the only point of the enclosure where they have been accessible.: L'architecture de l'enceinte urbaine du ive siècle
Curtain wall
The excavations conducted on Site 3 have enabled the identification of the internal structure of the wall. From the foundations, the curtain wall exhibits two distinct structural configurations.: Le mur de l'enceinte urbaine du ive siècle. Étude architecturale In the subsequent description, the numerals and letters in parentheses correspond to the markers illustrated in Figure I.
The initial course above the foundations comprises substantial blocks whose structural configuration is analogous to that of the foundations, albeit with a chamfered outer row (on average 0.30 meters). This initial course is surmounted by a series of rows of large blocks across the entire width of the wall (5), collectively forming the base (S) of the curtain wall.