This article examines the frescoes in the bell-tow­er chapel of the church of San Martino in Siena, the most important testimony to its Gothic phase. The initial uncovering of the paintings on the vault and walls, previously whitewashed, was car­ried out by the Sienese restorer S. Cresti between 1899 and 1903, in accordance with the principles established by G.B. Cavalcaselle, which exclud­ed any integration of missing portions. In 1922, the reopening of the chapel's Gothic single-light window led to the discovery of the 'Crucifix with Mourning Figures', painted in the niche below. In 1925, this work was restored by T. Baldini, who intervened extensively in the summary recon­struction of the missing parts, following the di­rectives of P. Bacci, who favoured reconstructive integration. The first comprehensive restoration of the complex, in 2000, concerned all the painted surfaces, also revealing six 'Apostles' painted on the intrados of the arch between the chapel and the presbytery area. Executed by restorers Giuseppe and Massimo Gavazzi, and Amedeo and Alessio Lepri, according to philological criteria, the in­tervention sought, as far as possible, to preserve the narrative function of the scenes and the illu­sionistic effect of the architectural structures and decorative framing. It is now possible to attribute the 'Apostles' to the Duccesque painter Segna di Bonaventura, while the 'Stories of Saint Leonard', several 'Saints', the 'Evangelists', and a 'Christ the Judge' may be regarded as an important commis­sion executed by Francesco di Segna in 1333 for the Agazzari family. The 'Crucifix with Mourning Figures', by contrast, appears to be the work of a collaborator of Simone Martini and Lippo Mem­mi, who adapted their inventions between the late 1310s and early 1320s.