This autograph letter from St Francis to Brother Leo, one of his earliest and closest followers, is kept in a reliquary in the Cappella delle Reliquie of the Duomo.   It is accepted as authentic, despite the fact that it went unrecorded until 1604, when it surfaced at SS Simone e Giuda.  When this church was suppressed in 1863, the letter again disappeared until 1893, when it came into the possession of Father Cardinali, the parish priest at San Filippo.  He referred it to Michele Faloci-Pulignani who in turn referred it to Pope Leo XIII.  The Pope established its authenticity and then entrusted it to the care of the Cathedral Chapter.  

The handwriting suggests that the letter was written in ca. 1225, when St Francis was nearly blind and suffering from the effects of the stigmata.  It seems to be in response to a conversation that the men had had “on the road”, which concerned a spiritual crisis that Leo was suffering.  It is addressed to "Frate Pecorello di Dio" (brother little sheep of God), and ends memorably: “And if you need and want to come to me for the sake of your soul or for some consolation, Leo, come.”