Petrarch made a collection of 350 letters he personally wrote called "Epistolae familiares" (a.k.a. Familiar Letters). In among these letters in 1346 Petrarch writes what is called "De vita solitaria", a treatise composed of two books and dedicated to Philippe de Cabassoles. In Book XXII of Familiar Letters is Petrarch's books of these letters to Philippe which he delivered 20 years after he wrote them. Also in addition to these books of letters he wrote some very special letters that he held out of the set of "Epistolae familiares", which was later put into a set of 19 letters called Liber sine nomine. Letters 1 and 12 are letters Petrarch wrote to his friend Phillippe that are in this reserved set of letters "without a name" of the recipient. Petrarch dedicated his work "De vita solitaria" to his friend Philip. A dedication to him is in the preface.