The Church's Year
Why is this Sunday called "Septuagesima"?
Because in accordance with the words of the First Council of Orleans, some pious Christian congregations in the earliest ages of the Church, especially the clergy, began to fast seventy days before Easter, on this Sunday, which was therefore called Septuagesima" - the seventieth day. The same is the case with the Sundays following, which are called Sexagesima, Quinquagesima , Quadragesima, because some Christians commenced to fast sixty days, others fifty, others forty days before Easter, until finally, to make it properly uniform, Popes Gregory and Gelasius arranged that all Christians should fast forty days before Easter, commencing with Ash-Wednesday.
Why, from this day until Easter, does the Church omit in her service all joyful canticles, alleluia’s, and the Gloria in excelsis etc?