"In those days Caesar Augustus issued a decree that a census should be taken of the entire Roman world. And everyone went to his own town to register. So Joseph also went up from the town of Nazareth in Galilee to Judea, to Bethlehem the town of David, because he belonged to the house and line of David. He went there to register with Mary, who was pledged to be married to him and was expecting a child."

Luke 2:1-5 (NIV)