The practice of honoring mothers started in ancient times, with societies tending to celebrate goddesses rather than real mothers.
In Egypt, there was an annual festival in honor of Isis, deemed to be the mother of the pharaohs, while the Romans feted Cybele, the great mother, who was based on Rhea, mother of most of the Greek gods, including Zeus.
With the advent of Roman Catholicism in the West, and the importance of Mary as mother of Jesus, the earlier pagan festivals were turned into a Christian celebration on the fourth Sunday of Lent.