This antiphonary (a book containing the choral parts of the Holy Office) was transferred to the Biblioteca comunale degli Intronati di Siena in 1811 from its place of origin, the Augustinian monastery of San Salvatore in Lecceto near Siena. By virtue of its specific liturgical function, the antiphonary, designed for the use of the monastic community, contains both the daytime and the nocturnal services. It was illuminated in 1442 as part of an extensive artistic program within the monastery promoted under priors Bartolomeo Tolomei and Girolamo Buonsignori. A bull by Pope Eugene IV in 1446 granted Lecceto independence from the Augustinian vicar general, placing it at the head of a vast network of monasteries. The peculiarities of the manuscript’s iconography, closely linked to the liturgical content, denote a specific visual program, undertaken especially for the Lecceto community. The Sienese painter Giovanni di Paolo has been definitively identified as responsible for completing most of the work’s illuminations. These are mainly historiated initials (decorated with people, animals, or scenes), but also include a depiction of the "Triumph of Death" placed at the beginning of the service for the dead (folio 162r). In this manuscript, the artist brings to fruition his extraordinary ability to render narrative scenes with striking originality. The other illustrations (five initials, of which four are historiated with a Marian subject and one is decorated) belong to a different hand in both technique and style and are the work of an extremely accomplished anonymous master. This master has been variously thought to belong to the Sienese school (the name of Priamo della Quercia has been suggested; so too has Domenico di Bartolo), the Umbrian school, or the Po Valley school.