http://billsey-christian.net/temp/MerryChristmas.html

As to certain references in the hymn, and which archaeologists are not likely to tell you publicly (but which I did find out from one of them) is that Jesus was not brought forth from Mary in a building, but in a sheepfold, most likely a cave, outside Bethlehem, and that the manger involved was most likely a ditch carved into the floor of that cave for use as a feeding trough (though it could also have been carved into a raised ledge within the cave), to feed the sheep, which makes it look as though the baby was lain in what could have looked very much like a shallow grave, or one of the Jewish tombs from around the area of Jerusalem or Bethlehem around that time. There is great symbolism there (John 6).