Jamieson, Fausset and Brown on 1 Samuel 5:2

2. the house of Dagon--Stately temples were erected in honor of this idol, which was the principal deity of the Philistines, but whose worship extended over all Syria, as well as Mesopotamia and Chaldea; its name being found among the Assyrian gods on the cuneiform inscriptions [Rawlinson]. It was represented under a monstrous combination of a human head, breast, and arms, joined to the belly and tail of a fish. The captured ark was placed in the temple of Dagon, right before this image of the idol.

1Sa 5:3-5. Dagon Falls Down.