local tradition held this as jesus' birthplace, and so in 326 a.d., helena, the mother of the emperor constantine, built the first church of the nativity here. it was restored by the emperor justinian in 529 a.d. and enhanced later on by the crusaders. well, i've also heard that the idea behind the door was to make people bow down. >> to be humble, yeah. it's not entirely -- it's not impossible, by any means. >> once inside this ancient building, visitors see a sight drastically different from the humble stable of the bible -- the greek orthodox main altar. very ornate. >> it's extremely ornate. you have the iconostasis. behind it is the altar, and then you see the choir stalls for the monks on either side. and this is where the liturgy is sung every sunday -- every day, in fact. >> the original church was an octagon, built over the venerated cave. it's now below the altar, in the grotto of the nativity.