This paper examines the connection between a XIIth century Old French hagiographical text (the Vie de Saint Gires by William of Bernevile) and a series of mural paintings, also dating back to the XIIth century, from the Loir Valley (France). Certain details, identified in these murals, seem to originate from William of Bernevile's poem. The Latin sources (the three versions of the Vita sancti Aegidii) omit them. The author analyzes the connections between these details, written or painted, and concludes that it is impossible to state whether the poem or any of the paintings were the first to be accomplished. Since both of them date back to the same period, one should imagine that these details of a different version of the Life of saint Giles are the results of a polygenesis.