Author and source is Jean-Claude Golvin:
https://people.unil.ch/cedriccramatte/files/2013/10/IAS-MAN-02871-3.jpg
https://jeanclaudegolvin.com/en/gallery/epomanduodurum-mandeure-the-castrum-of-the-late-roman-period/

I've upgraded the art via Waifu2x. Thanks to u/dctroll_ for this text:

The castrum of Mandeure was located in present-day Mandeure, in the French department of Doubs, next to the Doubs River, in the southwestern part of the ancient city of Epomanduodurum. Its construction began shortly before the mid-4th century AD, but the works were interrupted by the Alamanni invasion of AD 352 and later resumed and strengthened from AD 364, during the reign of Valentinian I. The fort covered approximately 1.5 hectares and had a distinctive bell-shaped layout. Its walls, which were up to about 4 metres thick at the base, were reinforced with semicircular and quadrangular towers.

Its strategic position along the Doubs River allowed it to control important communication routes and the supply of the military frontier along the Rhine. Archaeological evidence, including materials associated with the Legio I Martia, indicates a significant military presence. However, the castrum probably also had a civilian function and gradually became the new centre of Mandeure’s population during Late Antiquity.