Rogation days are, in the calendar of the Western Church, observed on 25 April (the Major Rogation) and the Monday, Tuesday, and Wednesday immediately preceding Ascension Thursday (the Minor Rogations).
Major Rogation 
The first Rogation, the Greater Litanies, has been compared to the ancient Roman religious festival of the Robigalia, a ritual involving prayer and sacrifice for crops held on April 25. The first Rogation is also observed on April 25, and a direct connection has sometimes been asserted, with the "Christian substitute" following the same processional route in Rome. If Easter falls on April 24 or on this day (the latest possible date for Easter), the Rogations are transferred to the following Tuesday.
Minor Rogations 
The second set of Rogation days, the Lesser Litanies or Rogations, introduced about AD 470 by Bishop Mamertus of Vienne and eventually adopted elsewhere, are the three days (Rogation Monday, Rogation Tuesday and Rogation Wednesday) immediately before Ascension Thursday in the Christian liturgical calendar. The term, most frequently encountered in Roman Catholic and Anglican circles, is rarely used today.
The word "Rogation" comes from the Latin verb rogare, meaning "to ask", and was applied to this time of the liturgical year because the Gospel reading for the previous Sunday included the passage "Ask and ye shall receive" (Gospel of John 16:24). The Sunday itself was often called Rogation Sunday as a result, and marked the start of a three-week period (ending on Trinity Sunday), when Roman Catholic and Anglican clergy did not solemnize marriages (two other such periods of marital prohibition also formerly existed, one beginning on the first Sunday in Advent and continuing through the Octave of Epiphany, or 13 January, and the other running from Septuagesima until the Octave of Easter, the Sunday after Easter). In England, Rogation Sunday is called Chestnut Sunday.
The faithful typically observed the Rogation days by fasting in preparation to celebrate the Ascension, and farmers often had their crops blessed by a priest at this time. Violet vestments are worn at the rogation litany and its associated Mass, regardless of what colour was worn at the ordinary liturgies of the day. A common feature of Rogation days in former times was the ceremony of "beating the bounds", in which a procession of parishioners, led by the minister, churchwarden, and choirboys, would proceed around the boundary of their parish and pray for its protection in the forthcoming year. This was also known as 'Gang-day'.
The reform of the Liturgical Calendar for Latin Roman Catholics in 1969 delegated the establishment of Rogation Days, along with Ember Days, to the episcopal conferences. Their observance in the Latin Church subsequently declined, but the observance has revived somewhat since 1988 (when Pope John Paul II issued his decree Ecclesia Dei Adflicta) and especially since 2007 (when Pope Benedict XVI issued his motu proprio called Summorum Pontificum) when the use of older rites was encouraged. Churches of the Anglican Communion reformed their liturgical calendar in 1976, but continue to recognize the three days before Ascension as an optional observance.
See also 
- Daniel T. Reff, Plagues, Priests, and Demons: Sacred Narratives and the Rise of Christianity in the Old World and the New (Cambridge University Press, 2005), p. 100 online.
- The Catholic Encyclopedia marks the connection; see the 1913 edition online.
- Greg Dues, Catholic Customs and Traditions: A Popular Guide (Twenty-Third Publications, 200, 2006), p. 39 online.
- General Norms for the Liturgical Year and Calendar arts. 45–47.