Ash Wednesday is the first day of Lent in the West. Pope Gregory I is credited with having introduced the ceremony that gives this day its name. When public penitents came to the church for forgiveness, the priest would take some ash (made by burning the palms used on Palm Sunday of the previous year) and mark their foreheads with the sign of the cross as a reminder that they were but ashes and dust. Eventually, the practice was extended to include all who wished to receive ashes. In the East, ashes are not used, and Lent begins on the Monday before Ash Wednesday. Discuss
Source: The Free Dictionary