Editio princeps of the famous work of Tolomei, which will count 23 editions during the sixteenth century. The 381 letters written by the Sienese Tolomei will be printed here with the orthography at the end of the volume, which made it possible to better distinguish the pronunciation, with the text in italics conforming to his phonetic theories. Also very interesting is the long letter addressed to Cesano with a description of the Argentario, considered by the author to be the ideal place to build a large city. The many letters addressed to Giambattista Grimaldi, a famous bibliophile, have served scholars to reconstruct the books in his famous library and above all the precious Apollo and Pegasus bindings that adorned them.