Caravaggio signed a contract in September 1600 to paint two large panels for a chapel in the Basilica of Santa Maria del Popolo, one showing the conversion of Saint Paul, the other the martyrdom of Saint Peter, for four hundred scudi. He delivered paintings that Cardinal Cerasi's heirs rejected outright, considered by early accounts too extreme for a church setting. What exactly made the first versions unacceptable is not recorded in enough detail to settle with certainty, but Caravaggio's habitual choices, harsh light, unidealized bodies, ordinary looking models standing in for saints, are the likeliest cause.
He painted the chapel a second time, and it is this second pair, on canvas rather than the cypress panels the original contract specified, that hangs there today. For Paul's conversion, Caravaggio stripped the scene down further rather than softening it, no crowd of onlookers, no angel visibly delivering a message, only Saul on his back in the dirt, a horse, and a groom who notices nothing unusual at all.
The paintings were finally installed by 1605, four years after the rejected originals, in a chapel Caravaggio's patron did not live to see finished. Whatever made the first attempt unacceptable to Cerasi's heirs, the second attempt has never since needed defending. It has hung in the same chapel, facing the same light, for more than four centuries.