Virgin and Child

Early 3rd century
Catacomb of Priscilla, Rome

This may be the earliest image of the Virgin Mary not in a representation of the Adoration of the Magi. The Christ Child (presumably) is nursing at his mother's breast while a man on the left points up at what could be a star. If these presumptions are true the subject of the fresco would be the Nativity and the man would be the prophet Balaam, whose prophecy of a star rising "from Jacob" (Numbers 24:17) was believed to foretell the star that would guide the Magi to the Christ Child.

Read more about portraits of Mary
Read more about images of the birth of Jesus.

Source: this page at Wikimedia Commons.