In the 5th century, St Augustine described a sacrament as "an outward and visible sign of an inward and invisible grace."
There are seven Sacraments: Baptism, Reconciliation, the Eucharist, Confirmation, Marriage, Holy Orders and Anointing of the Sick.
As Christ is the physical sign of God's love on earth, the Sacraments use physical symbols - water, oils, laying of hands... - as expressions of God's continuing grace in the world.