The phenomenon of plainsong masses, those polyphonic masses based on chants corresponding to the mass of a certain day or feast such as Missae paschalis, Missae dominicalis etc. still lacks a comprehensive overview. So far, studies have been conducted on individual masses and on groups of the same subtype as the Missae de beata virgine or the vast number of Heinrich Isaac’s musical settings of ordinary and proper chants. Similarly, the Missae de feria have not attracted attention aside from a first overview by Andrew Weaver. Based on his findings that the ferial masses can be grouped in distinct “families” – each characterised by stylistic uniformity and musical interconnections – I will focus on the cluster of Roman masses. These include the ferial masses by Johannes Martini, Andreas Michot and Johannes Beausseron as well as an anonymous mass cycle, preserved in the Sistine choirbooks CS 35, CS 55 and CS 63. Richard Sherr once drew attention to the fact that these very manuscripts also include some extraordinary settings of the Ash Wednesday tract Domine non secundum and suggested a liturgical-functional link to the Missae de feria. Following this trace in examining the chant models as well as the codicological, liturgical and musical connections between the Roman ferial masses and the aforementioned tract, I will provide a more precise perception of Missae de feria at the beginning of the sixteenth century.