High Quality Content by WIKIPEDIA articles! The Riom Trial (February 19, 1942 - May 21, 1943) was an attempt by the regime of Vichy France, headed by Marshal Philippe Pétain, to prove that the leaders of the French Third Republic (1870-1940) had been responsible for France's defeat by Germany in 1940. The trial was held in the city of Riom, and had mainly political aims, namely to project the responsibility of defeat on the leaders of the Popular Front government that had been elected in 1936.