The four horses that God’s messenger, Grace, gives Piers Plowman symbolize the four Fathers of the Western Church—Saint Augustine, Saint Ambrose, Saint Gregory the Great, and Saint Jerome. The four horses are meant to build on the work of the four oxen (the four Gospels) by pulling two harrows (the Old Testament and the New Testament) to further prepare the land for planting. In other words, the four Church Fathers are to prepare the institution of the Church by using the Gospels, along with the entire Old Testament and New Testament.
The timeline below shows where the symbol Four Horses appears in Piers Plowman. The colored dots and icons indicate which themes are associated with that appearance.