Scala/Art Resource, New York, NY

A mosaic lunette in the sanctuary of the Church of San Vitale, Ravenna (shown here, compare with next photo), shows two scenes from the life of Abraham, who lived with his wife Sarah beside the oaks of Mamre, near Hebron. In the first scene, the elderly couple stands to the left of an oak tree, with its carefully rendered leaves. Three haloed guests, seated at a table, announce to the couple that they will have a child within a year. Three loaves of bread lie on the table, and Abraham serves his visitors a calf on a platter. To the right, an older Abraham, his beard fuller and his hair whiter, stands with knife poised above his son. Out of the dramatic red sky reaches the hand of God. The ram tugs on Abraham’s robe—a reminder that he will be substituted for Isaac.