The moving back of the date of the cycle of mural paintings in the chapel adjoining the round church of San Galgano on Monte Siepi (which we now know were executed by Ambrogio Lorenzetti in 1334-1336) and confirmation of the identity of the chapel's donor (the Cistercian oblate Ristoro d'Orlando da Selvatella) allow us to reconsider the very nature of the Montesiepi cycle in a new light. Contrary to what has long been assumed, it should not be interpreted in the light of the last will and testament of a layman concerned about his own spiritual destiny, but rather in the context of the patronage (and spirituality) of the Cistercian monks. In addition to the painter's iconographic and stylistic experimentation, what emerges clearly from this new analysis of the cycle is that it is based on the integration of some important parts of the hagiography of Saint Galgano within the framework – which remains dominant – of the exaltation of the Virgin Mary as co-redeemer and Regina Coeli, therefore in line with the thinking of the leading Cistercian scholar, Saint Bernard of Clairvaux, and his followers. In the creation of the paintings of Montesiepi other influences were also decisive, such as the Marian laude, or sacred songs, that had been adopted within lay confraternities. Certain unprecedented iconographic expressions – it has been known for some time – were rejected by the Cistercian community, which a short time after the completion of the paintings had them modified by another painter. These were interventions – it is argued in the present essay – which had the precise function of making the meaning behind the cycle even more explicit.