Yves de Vallone’s manuscript treatise La Religion du chrétien conduit par la raison éternelle has become something of a landmark in the history of free thought, since it bears witness to the erratic intellectual career of its author. Initially a canon of the Congregation of Sainte-Geneviève, Vallone denounces a Socinian plot led by the directors of the institution. He is persecuted and eventually escapes to Switzerland, then to Germany and finally to Holland, where he arrives in Zwolle at the height of the Leenhof controversy. He embarks on a “metaphysical” defence of Calvinist doctrine but is sharply criticized by Jacques Bernard and sanctioned by the council of the Walloon Church. His reaction is to read Spinoza, Richard Simon and Bayle and launch into the composition of his treatise, which is a radical attack on Christian doctrine and history.