Natural hazards and building history: Roof structures of Segovia cathedral (Spain) reveal its history through tree-ring research

Abstract

Combined dendrochronological and archival research revealed the history of construction and subsequent repairs to the roof structures of Segovia Cathedral, the last gothic cathedral built in Spain. Although this iconic building has been extensively documented by different scholars, the completion date of the 16th century original sacristy was uncertain. Furthermore, disaster struck the building on two occasions, in the 17th and 18th centuries. First, on September 1614, lightning hit the bell tower and fire spread through the roof of the nave. Then, on 1 November 1755, the Lisbon earthquake shook the cathedral building. However, the extent of the damage caused by these events was unknown.Our combined research revealed that the trees used to make the tie-beams of the sacristy were cut in the late summer/winter months of 1676/77, one century later than the completion date, suggesting that this part of the original sacristy was renewed when a new one was built together with the offices in an annexed building. Furthermore, absolute dates obtained for the nave indicate that the trees used to build the current roof structure were cut in the autumn/winter of 1614/15, which implies that the 16th century original roof must have burned down entirely due to the lightning fire. A historical document registering the purchase of the wood to repair this structure in 1614 confirms this information. Finally, the damage caused by the Lisbon earthquake must have compromised the structural integrity of the roof, as the support timbers used to reinforce it belong to small trees cut in the spring or summer of that same year 1755. Archival research revealed that the roofs were inspected a few weeks after the earthquake, and that repairs were carried out in 1756. This suggests that the wood to prop up the structure was most likely purchased shortly after the inspection (probably in a nearby saw mill where cheap wood from trees cut in the summer of 1755 was available), and before the repairs took place.