The census that was ordered by Caesar Augustus was the first of its kind. It was done because the Roman government wanted to make sure that everyone in the Empire was paying their taxes correctly. The census was carried out all over Empire (most of Europe): but in Palestine, it was carried out in a Jewish way rather than a Roman way. This meant that families had to register in the their historical tribal town rather than where they lived. This also meant that Joseph and the very pregnant Mary would have had to travel from Nazareth to Bethlehem, as this was town that Joseph's family (the royal family of David) originally came from - a journey of about 70 miles.
Some people think that Bethlehem could also have been Joseph's actual home town and he'd traveled to Nazareth to collect Mary once they were betrothed/married to take to his home town to initially live.
The journey would have taken about three days and they might well have arrived in the evening, because if they had arrived earlier in the day, it is more likely that they would have found somewhere to stay.
Would you want to travel this far being pregnant? God again watched over them and brought them to Bethlehem safe. The first Christmas travelers to their hometown and family for Christmas. The tradition started once again with our LORD and Savior.
Hugs Prayers and God bless
Izzy
izzy