The Rogation Days are the "Monday, Tuesday, and Wednesday
before Ascension Day are observed by all Catholics of the Latin rite as days of
solemn supplication, and are called Rogation days because the Litany of the
Saints is chanted in the procession which takes place on each of the three
days, rogatio being the Latin equivalent for the Greek word litany. "
(Addis, W. E., & Arnold, T. (1887). A Catholic Dictionary)
The observance of the ʻRogation Daysʻ started in the 5th century
when St. Mamertus (who was Bishop of Vienne) instituted these ʻlitaniesʻ as a
public supplication asking God to hold back his wrath upon their city which had
gone through nearly half a century of various calamities. As most true
immemorial customs usually do, the example of the ʻRogation Daysʻ in Vienne was
soon followed in many places places throughout the world. It became a general observance throughout the Church soon after Pope Leo III introduced it in Rome in 816
image from the 'Public domain' via wikimedia commons. St. Valentine Kneeling in Supplication
