The timber roof of the central nave in the Basilica of San Michele in Pavia

A Basilica dedicated to Saint Michael was first built in the Longobardic period (6th-8th centuries), however the present building dates back to 11th-12th centuries. The church was built in Romanesque style and it is unanimously considered one of the masterpieces of the Lombard architecture of the period. During the subsequent centuries, the building underwent several changes and restoration works. Dealing with the roof of the central nave, the rebuilding of the vaults (1488-91) was the most relevant work. Traces of the pre-existent vaults are still visible in the attic; they were much higher than the present ones and thus they were incompatible with the structural organisation of the existing timber roof structure. Therefore the conception of this structural system probably dates back to that period. In 1860–75 the building underwent works of stylistic restoration and since the 1930s many preservation interventions were done in order to consolidate the decayed sandstone of the façades; however, these interventions did not affect the roof structures. In 1942 two reinforced concrete wall plates were built on the top of the longitudinal walls of the central nave and the timber trusses now lay on them. Since the early 19th century the church has been studied by many art and architecture historians, and many surveys and drawings have been done, both before and after the stylistic restoration works. However the historians’ attention has focused mainly on the formal features of the building and on the construction phases of masonry structure. In many of the drawings the roof structures are not even represented; in the others, they are only sketched out schematically. Therefore, the knowledge of the timber roof structures of the church is still very poor. In this situation, the study of archival documents and the survey and in situ investigation of the timber trusses play a fundamental role in the historical knowledge of this important but neglected timber structural complex. The structural complex is composed of a sequence of seven quite different trusses supporting the upper layers of timber elements (i.e. purlins, joists and laths) and the roof tiles. The paper advances a hypothesis about the dating of each of the trusses, based on the matching of the archival data with the critical interpretation of the surveyed signs: structural type of the truss, type of joints, signs of woodworking tools (e.g. axes, saws, hand drills, chisels), assembly marks, signs of reutilization of timber elements, type of iron reinforcement elements, etc.