Reports work carried out to make the various structural parts of the San Casciano theater in Tuscany, Italy, statically functional. Owing to failure to maintain the roof, some of the wooden structures risked being completely lost. Explains the stiffening method used for the wood joists for the three circles on which a mixed wood-concrete working system was built with steel shear bracing, prestressed to reduce seismic risk. Describes technologies used to rebuild some of the ribbing in the acoustic vault, to strengthen the ribs and matting of the vault itself, and to reinforce the great trusses.