In Luke chapter 2 verses 1 through 7, we learn that Caesar Augustus decided it was time to institute a new tax on all the lands ruled by the Roman Empire. In order to enforce the decree, all the people must be accounted for and they must return to their homeland to be registered so they could participate in a census.
By counting the people under their rule, Caesar would have an indication of how much money he would raise and where to set the rate to maximize his return. This act though had an other pre-planned effect, Joseph and a pregnant Mary would be forced to return to Joseph's birth land, Bethlehem.
The journey would take about 9 days over 90 miles. Unlike traditional stories, Mary most likely walked the entire way. The bible doesn't tell us how they managed to carry their supplies, maybe a donkey was involved, maybe Joseph carried what he could and stopped at merchants along the way. Either case, the journey was tough enough, even harder because Mary was at full term.
Today is December 24, 2012, about 2009 years ago in 3 AD, give or take a few years and six months, Joseph, Mary and the soon to be born baby Jesus was on the outskirts of Bethlehem. Because of the census, all the hotels, a.k.a. inns, were already full. Tomorrow they would end up in a cave like manager, where the love of the world would enter the world and save everyone from our sins.