When Mary was pregnant, she and Joseph had to go on a long journey, so that the Roman Caesar Augustus ordered a census of the population throughout its land. Everyone had to go to the city of his ancestors. Joseph and Mary were out of the house and lineage of King David. David's hometown was Bethlehem. King David of Israel rules over a thousand years before Jesus was born.
So Joseph and Mary went to Bethlehem, the city of his ancestor David. From Bethlehem to Nazareth, more than two hundred kilometers. While there was not a train or car, and this lasted for several days journey. Nazareth is located in the north of Israel, in the Galilee and Bethlehem - in the south, in Judea. Going from Galilee to Judea, and it was necessary to pass through Samaria. And Samaria and Judea - mountain terrain.
When, finally, Joseph and Mary arrived in Bethlehem, was not there at the hotel. Many came to Bethlehem for the census. Mary also is the time to give birth. "... And she brought forth her firstborn son, and swaddled him and laid him in a manger," we read in the Gospel. This means that they were placed in a pen for livestock. According to ancient tradition, the crib was in the cave. In those places, and is currently used for the shepherds of his sheep are caves.