On medieval building sites, marks left on stone by the tools during construction are very useful indicators in understanding the organization and level of specialization of stonemasons. In the province of Siena in particular, between the late 12th and the early 13th century, we witness the diffusion of ‘new’ tools with toothed blades (toothed chisel-end hammer, toothed chisel, ciseau grain d’orge), used by specialized craftsmen of Pisan-Lucchese formation working in the main settlements of the upper Val d’Elsa, in the abbey of San Galgano in the Val di Merse and in Siena cathedral. After the mid-13th century these implements circulated widely, until they became standard tools of the trade used by Sienese craftsmen.