Bethlehem, just south of Jerusalem, is considered the birthplace of Jesus. The Church of the Nativity, which commemorates the birth, was originally built at this site in the fourth century AD. It was built by Queen Helena, the mother of Constatine the Great, the first Roman Emperor to embrace Christianity. The Church has been rebuilt many times since then, though a remnant of the fourth century mosaic floor survives. There are several other sites of religious import in Bethlehem as well. On Christmas Eve, there is always a large celebration in Manger Square, Bethlehem's central plaza. This is also the site of the matriarch Rachel's Tomb, and the shepherd's field where the angel appeared to announce the birth of Jesus. The field is also known as the Field of Ruth, daughter-in-law of Naomi in the Biblical Book of Ruth, who adopted the faith of her Jewish mother-in-law and whose great grandson David became the psalmist King of David.