According to the Roman Gemellus, King David built the Israelites' First Temple in Jerusalem "between five and six hundred years" before the year 64. (PROSE: Byzantium!)
Jewish tradition held that the Messiah would be a descendant of David and Solomon, and that he'd be born in Bethlehem. When Jesus of Nazareth fit these criteria, a small sub-sect of Judaism called Christianity was formed; they maintained that Jesus was the aforementioned Messiah, their saviour. (PROSE: Byzantium!)
According to Emporator Tannalis, David had extra-marital relations with a woman named Abishag. He thought he couldn't get away with a similar thing. (PROSE: Halflife)
Behind the scenes
The sculpture seen in The Girl Who Waited noticeably has the controversial fig leaf censoring David's visible penis, which is curiously only used in the Victoria and Albert Museum reproduction, effectively making the Apalapucia one a reproduction of a reproduction. Even more interestingly, a sculpture with visible breasts was not only seen earlier in the episode, but was focussed on in dialogue.