Fighting and dying for one’s faith. Joseph-Louis Guérin (1838-1860), seminarian, papal soldier and ‘martyr’

What can lead someone to take up arms on behalf of his faith and to sacrifice his life to a religious cause? The article addresses this topical issue by looking at one individual’s itinerary: Joseph-Louis Guérin (1838-1860). This young seminarian from Nantes abandoned his ecclesiastical studies in July 1860 to join the Pope’s Army, and was killed in the battle of Castelfidardo a few months later. From the sources provided by his biographies and the records kept in the archives of the Diocese of Nantes, this article attempts to understand Guerin’s decision to enlist and his proclaimed aspiration to self-sacrifice in the light of the great Catholic mobilisation of winter of 1860 and of an uncompromising religious culture that conveyed a form of radicalism.