De pictura by Leon Battista Alberti (1404?-1472) is the earliest surviving treatise on visual art written in humanist Latin by an ostensible practitioner of painting. The book represents a definitive moment of cohesion between the two most conspicuous cultural developments of the early Renaissance, namely, humanism and the visual arts. This dissertation reconstructs the intellectual and visual environments in which Alberti moved before he entered Florence in the curia of Pope Eugenius IV in 1434, one year before the recorded date of completion of De pictura. For the two decades prior to his arrival in Florence, from 1414 to 1434, Alberti resided in Padua, Bologna, and Rome. Examination of specific textual and visual material in those cities - sources germane to Alberti's humanist and visual development, and thus to the ideas put forth in De pictura - has been insubstantial. This dissertation will therefore present an investigation into the sources available to Alberti in Padua, Bologna and Rome, and will argue that this material helped to shape the prescriptions in Alberti's canonical Renaissance tract. By more fully accounting for his intellectual and artistic progression before his arrival in Florence, this forensic reconstruction aims to fill a gap in our knowledge of Alberti's formative years and thereby underline impact of his early career upon his development as an art theorist.