Themes: Mixed Classical and Biblical
Here is an example of how artists mixed classical themes with religious themes. Here was have the shepherds adoring the Christ child (the three kings are coming down the road). This is actually a great mix because it has classical elements, biblical elements, and all set in an obviously Italian countryside. The people in the painting, except for Mary and Joseph, are dressed as Italians.
The town in the background is an Italian town, but the triumphal arch is very much Roman. I especially like the Corinthian columns supporting the roof of the manger!
The artist has inscribed the year of the painting at the top of one of the columns: 1485.
In terms of composition, what's Joseph looking at? At first I thought it was the on-coming horde -- they'll probably want to stay for lunch! -- but he's looking above that. See the angel, announcing the birth to the shepherds on the hill?