Castellum de Larçay, Roman military fortification in Larçay, France

Castellum de Larçay is a Roman military fortification with a trapezoidal layout and walls reaching approximately 6 meters high with varying thickness between 2.2 and 4.2 meters. The structure occupies a hillside overlooking the Cher River and once guarded several ancient trade routes in this region.

Built in the second half of the 3rd century, the castellum replaced a monumental mausoleum whose columns were reused in its foundations. It was abandoned at the end of Antiquity, and its construction was never finished. Its purpose was to watch over the Cher River and the roads near Caesarodunum (Tours).

The site's name comes from the Latin castellum, meaning a small fort. The fort was built on the site of a monumental mausoleum, and its builders reused the mausoleum's fluted and smooth columns in the foundations and lower courses of the walls. Louis Boilleau noted this reuse in 1865, though the columns' origin was then unknown.

The site is accessible via the surrounding paths and offers good views of the overall structure from the exterior. The best time to visit is during clear weather when the details of the walls and their layering are most visible.

Archaeological work between 1984 and 1987 revealed that the northern wall remained unfinished at foundation level. This discovery suggests the construction project may have been interrupted or never fully completed for reasons still unclear.