Riom (rēôN`), town (1990 pop. 19,302), Puy-de-Dôme dept., S central France, in Auvergne. It has distilleries, tobacco plants, and factories making pharmaceuticals. Of Gallic origin, the Roman Ricomagus grew around the collegiate Church of St. Amable (1077; restored). It was the capital of the dukes of Auvergne. In 1942, Riom was the scene of an abortive trial of French leaders (including Blum, Daladier, and Gamelin) by the Vichy government. The defendants, charged with plunging France into World War II unprepared, produced evidence placing the guilt on their accusers, and the trial was recessed.