Originally, the first day of Lent was the day on which public penitents at Rome began their penance. They were sprinkled with ashes, dressed in sackcloth, and required to remain apart from the community until Maundy Thursday (the Thursday before Easter).
As this practice fell into disuse between the 8th and 10th centuries, it was replaced by the general penance of the entire congregation.
From at least as early as the 8th century, this day was known as dies cinerum (day of ashes). This reflects the central ritual of this holiday, the placing of ashes on the forehead to symbolize mourning and penitence.
This ritual continues in the Roman Catholic Church today. Anglican, Lutheran and some other Protestant churches also hold a special worship service on Ash Wednesday, but do not usually include the ritual of ashes on the forehead. In Eastern Orthodoxy, Lent begins on a Monday known as “Clean Monday.”