The bridge itself (in both Wilder's story and Mérimée's play) is based on the great Inca road suspension bridge across the Apurímac River, erected around 1350, still in use in 1864, and dilapidated but still hanging in 1890. When asked by the explorer Victor Wolfgang von Hagen whether he had ever seen a reproduction of E. G. Squier's woodcut illustration of the bridge as it was in 1864, Wilder replied: "It is best, von Hagen, that I make no comment or point of it." In fact, in a letter to Yale professor Chauncey Tinker, Wilder wrote that he had invented the bridge altogether. The name of the bridge is drawn from the Mission San Luis Rey de Francia in San Diego County, California.