| On the basis of an extensive manuscript research, a new interpretation of the tracts that Bartolus de Saxoferrato wrote between 1355 and his death（1357） has been advanced. The four tracts（De Tiberiadis, De regimine civitatis, De Guelphis et Gebellinis, and De tiranno）that circulated as separate entities after the death of their author had been conceived by the author as a single work. An example of the original work, as intended and written by the author, has been identified in a manuscript now housed in the Library of the University of Harvard（Law School）. The autograph copy of the first tract of this series, De Tiberiadis, has also been identified and is now housed in the Biblioteca Apostolica Vaticana, Barberini Collection. As a consequence these tracts cannot be studied as separate entities but must be considered, studied, and published as a unity. In addition, the first instance of an interdisciplinary study mixing law and Euclidean geometry produced by a medieval jurist has been brought to the light. Last but not least, the tract De Tiberiadis is a good example of the attention medieval jurists devoted to environmental issues－in this cases, the problems caused by the changes occurring in rivers. |