Rogation Days, from the Latin word  rogatio, meaning Litany, because the Litany of the Saints is chanted in those days in the processions which take place.

The Rogation days originated in France. In the year 469 AD the city of Vienne suffered from earthquakes, failure of crops, and other calamities. The pious Bishop  Mamertus, who saw in the events the judgement of God, called upon his flock to appease Heaven by penances, processions and prayers during the three days before the Ascension day. The example of Mamertus was followed by all the French bishops and the custom finally became general. These three Rogation days serve also as a preparation for the feast of the Ascension, which reminds us that we have the most powerful intercessor on Our Savior, Who is now enthroned at the right hand of the Father.

This truth come from Goffine Devout Instructions on Epistles and Gospels printed in 18th of July 1669, I'll have this 722 page book available for download soon.