The Philistines captured the Ark of the Covenant and placed it in the temple of the idol Dagon in Ashdod, but the Lord caused the idol to be smashed and its worshippers to be plague-stricken. Old Testament (I Samuel 5: 1-6). On the left are the Ark of the Covenant and the broken idol of Dagon.
This is a copy of Poussin's original of 1630-1 (Paris, Louvre), but with differences in the background. These differences may reflect an earlier idea for the background in Poussin's picture.