At Rome during the 4th to 6th century, Holy Thursday was a day for the reconciliation of the penitents. In the 7th century, there were two Masses in churches celebrated by priests: one in the morning to close out Lent, and the other in the evening to commemorate the institution of the Eucharist. But during noon, a Mass was celebrated by the Pope (=Bishop of Rome) and consecrated the chrism and blessing the oils. The ministers were also instructed to reserve a portion of the "sacrifice" consecrated in this Mass for the next day: reservant de ipso sacrificio in crastinum unde communicent, as the Gelasian notes in its rubrics.
The Sacramentary contains the propers for three Masses: one for the closing of Lent, another for the chrism, and yet another for the Last Supper.