Analysing the medieval roof of the San Francesco's church in Prato (Italy): A dendrochronological interpretation

The church of San Francesco was built on terrain donated by the city of Prato to the Franciscan Friars just 2 years after the saint's death. In addition to worship, the building is of extreme historical and architectural interest and preserves valuable medieval artwork inside. The roof structures show modern features combined with ancient decorations and elements, which do not allow to precisely define its chronology. In particular, it is not clear whether the current roof structure dates back to the original construction or is the result of repeated subsequent interventions. The dendrochronological investigation involved 49 structural elements collected from 14 of the 16 trusses. The results obtained from silver fir samples separated the material into two groups: an older one, with a terminus post quem dating back to 1278, and a more recent one, which is the result of interventions of the mid-nineteenth century. The oldest elements are essentially the tie-beam of the trusses, while the replacement interventions have affected the rafters and some prostheses of the tie beams. The dendrochronological analysis showed marked analogies between the oldest roof structure of the church of Prato and that of the Basilica of Santa Croce in Florence, suggesting that the timber could comes from the large silver fir forests of Casentino, in Tuscany