Traditional belief is that Melchizedek had buried Adam’s skull at Golgotha where Jesus’ crucifixion took place. According to Jewish tradition, Noah confided the skull of Adam to his son Shem, who later did the same to Melchizedek.
Melchizedek deposited the skull at the mountain that came to be known as Golgotha because of the skull of Adam. Some early Christian writings also give similar accounts. That is why the artists depict the skull of Adam at the foot of Christ’s cross to show that the blood fell on the skull of Adam from the crucified body of Jesus compensated Adam’s sin. This was the fulfillment of God’s promise to Adam that he would send a redeemer (Gen 3:15).
Jesus removed the original sin the humanity inherited through his sacrifice on the cross. We got its merit through the Sacrament of Baptism. However, Satan who tempted the first parents continues his work in the world until the second coming of Christ. So, we must be watchful, and in case of failure, we should approach Jesus for forgiveness through the Sacrament of Reconciliation.