According to generally accepted Christian tradition, it was because there was a Roman census and Joseph had to return to his home town. A biblical passage from Luke (Chapter 2) supports this. * 1 And it came to pass in those days, that there went out a decree from Caesar Augustus that all the world should be taxed. * 2 And this taxing was first made when Cyrenius was governor of Syria.) * 3 And all went to be taxed, every one into his own city. * 4 And Joseph also went up from Galilee, out of the city of Nazareth, into Judaea, unto the city of David, which is called Bethlehem; (because he was of the house and lineage of David:) * 5 To be taxed with Mary his espoused wife, being great with child. * 6 And so it was, that, while they were there, the days were accomplishe