The aim of this research – which parallels the investigations on the former Spinelli chapel – was to re-examine the 14th-century frescoes of the Petroni chapel in Santa Maria dei Servi, Siena, in the complex context of the strategies of this mendicant order's establishment in the territory and the construction of one of the city's main church buildings. After a brief summary of the settlement of the friars in Siena, attention is focused on some fundamental events occurring in the late 13th century, when the ground was being prepared for their consolidation in the city. The Servite community assumed a primary role in municipal religious life, on a par with the other mendicant orders; it enjoyed the economic support of the city magistrature, and municipal disbursements were decisive for the financing of the 14th-century building. These, together with bequests from private donors, as well as evidence provided by the architectural structures and the remains of the oldest painted decorations, have made it possible to gather information on the progress of the architectural work in the first half of the 14th century. In particular, the second sacellum to the right of the high altar has been analyzed here, whose patronal rights were acquired ab initio by the Petroni family: a veritable noble chapel, it was the burial place of numerous members of the family and the object of repeated bequests pro remedio animae. The focus of the research has been an analysis of the 14th-century frescoes, which formed part of the chapel's iconographical programme, the authorship of which has been a never fully resolved critical issue.