"Nor would the Emperor let him depart without a further sign of royal favour, for he was commanded to write a Mass, an offertorium, and a trumpet concerto to celebrate the dedication of a new chapel in the city."
"_Offertory_ (sometimes spelled _offertoire_, or _offertorium_) -- a piece of music played or sung during the taking up of the offering in the church service."
"The Gregorian Sacramentary contains only the rubric: "deinde offertorium, et dicitur oratio super oblata""