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Origin and history

The Gallo-Roman enclosure of Nantes, built around 276 under the Emperor Tacite and completed by Probus, lined the ancient town of Portus Namnetum (now Bouffay district). It was 1,665 metres long and included circular towers and poternes, with small apparatus trims typical of the Lower Empire. Its foundations, composed of rubble and bricks drowned in mortar, reflect the Roman techniques of the time, visible today in the remains near the cathedral and the convent of the Cordeliers.

In the 9th century, the enclosure did not resist the Norman attacks, resulting in its partial reconstruction in the 10th century by Bishop Foucher, then its repeated destruction. In the 13th century, Guy de Thouars and Pierre Mauclerc, Duke of Brittany, dismantled much of the Roman walls to erect new medieval fortifications. Only the sections along the Erdre and the Loire remained until the modern era, before gradually disappearing with urban expansion.

The current remains are limited to three sites: the Saint-Pierre Gate (classified in 1926), an 18-metre stretch in the courtyard of the Saint-Pierre school, and an exhibit at the Nantes Museum of History. These relics, some of which were searched at the beginning of the twentieth century, illustrate the defensive evolution of the city, from the barbaric invasions of the third century to the Norman raids. The medieval chapel dug in the enclosure, classified as a historical monument, bears witness to its subsequent reuse.

The construction of the enclosure met an urgent need for protection in the face of the invasions of the third century, as evidenced by the Milestones dating from 276. Its route, marked by towers of 8 meters in diameter, married the natural contours of the Loire and the Erdre, integrating strategic doors like that of Saint-Pierre. Construction techniques, combining squared bellows and brick chains, were similar to those observed in other cities of the Empire from London to Constantinople.

In the Middle Ages, the enclosure gradually lost its defensive role in favour of ramparts on the ground (like that raised by Alain Barbe-Torte around 940) or medieval walls. Successive demolitions, particularly to enlarge the cathedral in the 10th century, reduced its grip. In the 19th century, the last visible remains (place du Bouffay, rue Saint-Léonard) disappeared, leaving only the present fragments, protected for their historical and architectural value.

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