A 1987 movie by Ruggero Deodato.

Two twin brothers are separated by king Kadar when he conquers their kingdom, reducing queen Canary to slavery. His sorceress, China (Sheeba Alahani) plots to have the two twin brothers fight to death in the arena, but it fails, and the heroes escape. Sent after them, to find the sacred diamond of Canary, China and Kadar's captain of the guards are eaten by a giant swamp monster. Later, the twin brothers manage to kill the monster to retrieve their sacred jewel from the hands of China, inside the beast's throat.