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Heritage classified

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Origin and history

The Gallo-Roman temple of Izernore, classified as a historical monument since 1840, is a religious complex built between the middle of the 1st and the end of the 2nd century AD. It consists of two successive buildings erected at the same location, the second partially reusing the structures of the first. Although the excavations did not allow their exact appearance to be reconstructed, the remains still visible (three columns of angle and scattered blocks) belong to the second, more imposing temple. This monument, linked to the ancient agglomeration of Isarnodurum, bears witness to a larger cultural site, including potentially thermal baths, wells and a hypothetical theatre.

Archaeological studies reveal an occupation of the site even before the temples were built, attested by Gaulish coins, but its extent remains unknown. The first temple, probably built under the Flavian dynasty (second half of the first century), has a level structure surrounded by a colonnade, while the second, peripter on the podium, measures about 19.20 × 22.60 m. Its excreted cella and doubled walls suggest a cultural continuity during the works. Painted decorations, with fragments remaining, used Spanish cinnabar, an expensive pigment, and represented geometric, plant and animal patterns.

The identity of the venerated divinity remains uncertain, although hypotheses evoke Mercury (after a votive inscription found in 1650), Roma (linked to a bronze finger discovered in 1825), or Mars (based on a disputed local toponymy). Abandoned at the end of antiquity, the temple was looted for the recovery of its materials, but its three angular pillars, 8 m high, strangely escaped this destruction. The first descriptions of the ruins date back to the 6th century (Life of the Fathers of Jura), followed by studies by local scholars in the 17th and 18th centuries.

Systematic excavations began in 1783 under the direction of Thomas Riboud, then continued in the 19th century, financed by the State and the department of Ain. In 1910, a controversial restoration partially rebuilt the walls, compounding the interpretation of the remains. Modern research, such as that carried out by Raymond Chevallier in the 1960s, helped to clarify the chronology and organization of the site. In 2013–14, new investigations completed this data, leading to a consolidation of the ruins in 2015. Today, the temple, the only Gallo-Roman vestige visible in the Ain, is protected and accessible to the public, while a stylized replica adorns the southern entrance of the commune.

Archaeological furniture (currency, fragments of statues, inscriptions) is preserved at the museum of Izernore, created in 1908 and labeled Musée de France in 2003. Among the notable pieces are a fragment of petase (attribute of Mercury) and a statuette interpreted as Sucellos, the Gaulish god. Despite its importance, the temple of Izernore still raises questions, including its connection to the Battle of Alésia, a 19th century hypothesis in a post-1870 nationalist context, or the exact function of neighbouring wells, originally considered rituals before being reinterpreted as domestic.

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