In his incessant hunt for books, Leonardo pursued some of the great ancient and modern masters who were crucial models for his research: Archimedes, Vitruvius, and Leon Battista Alberti. One of the modern masters, Sienese engineer Francesco di Giorgio Martini (translator of Vitruvius), became his friend. Leonardo intensively studied the two editions of Francesco’s Treatise, which is also the only surviving book from his library with marginal notes in Leonardo’s own hand.