The research starts from reconstruction of Giovanni Giacomo Leonardi’s biography, as a military engineer, ambassador and knight, born in Pesaro, who served the dukes of Urbino Francesco Maria I (1490-1538) and Guidobaldo II (1514-1574) della Rovere. By the analysis of the sources between Pesaro, Florence and Venice, the thesis collocates Leonardi’s figure in the Italian XVI century scenery, in order to mark the importance of his thirty-two books treaty, titled “Il Principe Cavalliero”, dedicated to art of war, diplomacy and honor science.
As most of the original treaty has remained unpublished, the books concerning honor science and ambassery have been transcribed and studied in order to prove how effectively and efficiently the rules of “religione di cavalleria” were applied amidst gentlemen’s and nations’ relationships.