Bethlehem lies 10 kilometers south of the city of Jerusalem, in the fertile limestone hill country of the Holy Land. Since at least the 2nd century AD people have believed that the place where the Church of the Nativity, Bethlehem, now stands is where Jesus was born. One particular cave, over which the first Church was built, is traditionally believed to be the Birthplace itself. In locating the Nativity, the place both marks the beginnings of Christianity and is one of the holiest spots in Christendom. The original basilica church of 339 AD (St Helena), parts of which survive below ground, was arranged so that its octagonal eastern end surrounded, and provided a view of, the cave. This church is overlaid by the present Church of the Nativity, essentially of the mid-6th century AD (Justinian), though with later alterations. It is the oldest Christian church in daily use. Since early medieval times, the Church has been increasingly incorporated into a complex of other ecclesiastical buildings, mainly monastic.