Septuagesima comes from the Latin word for "seventieth," with Sexagesima and Quinquagesima equalling "sixtieth" and "fiftieth" respectively. They are patterned after the Latin word for the season of Lent, Quadragesima, which means "fortieth" because Lent is forty days long (not counting the Sundays, which are all considered little Easters). Because a week is only seven days long, not ten, and since even then only six of those days might be counted if the pattern of Quadragesima is followed, Septuagesima, Sexagesima, and Quinquagesima obviously don't literally correspond to the periods of time they imply.
The 17-day period beginning on Septuagesima Sunday was intended to be observed as a preparation for the season of Lent, which is itself a period of spiritual preparation for Easter. In many countries, however, Septuagesima Sunday still marks the traditional start of the carnival season, culminating on Shrove Tuesday, more commonly known as Mardi Gras (literally Fat Tuesday, because it was the last possible opportunity where one could hold a feast and indulge oneself before the onset of Lent).
In the pre-1970 Roman liturgy, the Alleluia ceases to be said during the liturgy, effective at Compline on the Saturday before Septuagesima Sunday, not to be sung again until Easter. Likewise, violet vestments are worn, except on feasts, from Septuagesima Sunday until Holy Thursday. As during Advent and Lent, the Gloria and Te Deum are no longer said on Sundays.
Because of this temporary discontinuance of the Alleluia in liturgical functions, the liturgical office on the eve of Septuagesima was performed in many churches with special solemnity, and Alleluias were freely inserted in the sacred text (the Roman Breviary notes that after the "Benedicamus" of Vespers two Alleluias are to be added, instead of the usual one), even to the number of 28 final alleluias in the church of Auxerre in France.
This custom also inspired some poems which were sung or recited during Vespers in honor of the sacred word. The best-known of these hymns is Alleluia, dulce carmen (Alleluia, Song of Gladness), composed by an unknown author of the 10th century.
In fact, in a number of places (such as in some areas of France or Germany) during the Middle Ages, there was also developed an elaborate ritual called the "burial of the Alleluia", in which the Alleluia was symbolically "buried". We find the following from a 15th century statute book of the Church of Toul:
On Saturday before Septuagesima Sunday all choir boys gather in the sacristy during the prayer of the None, to prepare for the burial of the Alleluia. After the last Benedicamus they march in procession, with crosses, tapers, holy water and censers; and they carry a coffin, as in a funeral. Thus they process through the aisle, moaning and mourning, until they reach the cloister. There they bury the coffin; they sprinkle it with holy water and incense it; whereupon they return to the sacristy by the same way.In Paris, meanwhile, a straw effigy bearing in golden letters the inscription "Alleluia" was brought out the church yard and burned. In other areas, a banner or a scroll carrying the word was taken out and hidden or buried. While this custom had largely disappeared, some Lutheran churches preserve it, practicing it on the Sunday preceding Ash Wednesday (Transfiguration Sunday according to the Lutheran calendar).
In other liturgical rites the situation is a bit different. In the Ambrosian Rite, practiced in Milan and surrounding areas, there are three pre-lenten Sundays as in the Roman Rite (also named Septuagesima, Sexagesima and Quinquagesima), but these are only semi-penitential: during Sunday Masses the Gloria and the Hallelujah (the preferred spelling of Alleluia in the Rite) are retained. As there is no Ash Wednesday in the Ambrosian Rite, the liturgical Lent, with its use of litanies (the Divinae Pacis and the Dicamus Omnes) on Sundays instead of the Gloria in Excelsis and the disuse of Hallelujah, began on the first Sunday, with the fast commencing on Monday.
In the Mozarabic Rite (Spain), meanwhile, nine Sundays are given after the feast of the Epiphany, the last being called Dominica ante Cineres ("Sunday before the Ashes") or Dominica ante Carnes Tollendas ("Sunday before the Farewell to Meat"), the rest being numbered one to eight "Post octavam Epiphaniae" ("After the Octave of the Epiphany"). Ash Wednesday ("Feria Quarta In Capite Jejunii") is an evident late Roman borrowing, rather clumsily inserted, since the Sunday that follows, though called "Dominica prima Quadragesimae" ("First Sunday of Lent"), has a Mass and an Office in which Alleluia is used, and at Vespers there is the well-known "Endless Alleluia" (Alleluia Perenne) hymn. In the Mozarabic Hymnal this hymn is entitled "Ymnus in carnes tollendas" ("Hymn at the Farewell to Meat"). The true liturgical Lent does not begin till the Monday after Ash Wednesday, as was originally the case in the Ambrosian. The post-revision Rite however seems to have dropped Ash Wednesday and now considers Lent to begin with the First Sunday of Lent in Carnes tollendas, which can occur somewhere between February 11 to March 14, depending on the year.
READINGS FOR THE THREE SUNDAYS (from the pre-1970 Missal)
1.) Septuagesima Sunday (Missa Circumdederunt Me)
Introit: Psalm 17:5-7, 2-3 (8:4-6; 1-2)
Epistle: 1 Corinthians 9:24-27; 10:1-5
Gradual: Psalm 9:9-10, 18
Tract: Psalm 129:1-4 (130:1-4)
Gospel: Matthew 20:1-16
2.) Sexagesima Sunday (Missa Exsurge)
Introit: Psalm 43:23-26, 2 (44:23-26, 1)
Epistle: 2 Corinthians 11:19-33; 12:1-9
Gradual: Psalm 82:19, 14 (83:18, 13)
Tract: Psalm 129:1-4 (130:1-4)
Gospel: Luke 8:4-15
3.) Quinquagesima Sunday (Missa Esto Mihi)
Introit: Psalm 30:3-4, 2 (31:2-3, 1)
Epistle: 1 Corinthians 13:1-13
Gradual: Psalm 76:15, 16 (77:14, 15)
Tract: Psalm 99:1, 2 (100:1, 2)
Gospel: Luke 18:31-43