Among the manuscripts of Pope Clemente XI Albani’s Archive, there is the Tractatus de algebra seu de arte rei et censui by Paolo da Middelburg (1445-1534), with marginal notes and calculations by Muzio Oddi, to whom the codex belonged. The treatise is very interesting for several reasons. Firstly, it shows Paolo skill in algebra: so far scholars were still unaware of such a skill. In fact, until now Paolo was merely known as the astronomer-astrologer of the Dukes of Urbino, as well as court physician, primarily dedicated to the calendar reform. Secondly, the treatise is important because it enriches the range of mathematical interests of the duchy, which, as far as the works by Commadino, Guidobaldo and Muzio Oddi are concerned, were not particularly developed in Algebra. Thirdly, it is a further step to rebuild the long process that led Algebra to be, during the sixteenth century, the first field of research which overtook and outpaced the mathematics of the Greek classics. Paul’s Algebra shows a very high quality with respect to the average knowledge of that period, especially as regards the expositive form of the rules resolving the single equations: Paolo reduces the cases of equation classifications and it adopts a synthetic exposition and a comprehensive approach. These characteristics make his work something rare for time.

Key-words: Calculus; Equations; Generalization