St. Mark’s Day is the old Roman Festival of the Robigalia, the observance of which was magickally intended to avert the spirit of mildew, which threatens crops around this time. For many years, the Litania Major of the Catholic church for St. Mark’s Day at Rome followed the earlier festival. Its purpose, like the Robigalia, was to gain the blessing of heaven for the growing crops. In traditionally English lore, this is Cuckoo Day. The cuckoo, “St. Mark’s gowk,” heralds the arrival of migratory birds from the south, indicating the return of summer.
The Pagan Book of Days