He went to register there, together with Mary, who was pledged in marriage to him and expecting a baby.
It was the time when Caesar Augustus issued a decree that there should be a census of everyone in the Roman Empire.
So everybody went to their own city to be registered.
Joseph was descended from King David, so he left Nazareth in Galilee to go to Bethlehem, the city of David, in Judea.
While they were there, the time came for her to have her baby.