They are not vampires, for one thing. You have to find out which canto from the poem that this painting illustrates to find out who these naked guys are and why they are fighting. They're in Hell...
Aha! After some searching, I found this:
Bouguereau's masterpiece of dynamic composition, a scene from 'Dante's Inferno.'
In the Fifth Circle of Hell, on the banks of the River Styx, those damned for the sin of wrath fight each other through eternity, while the sullen and slothful languish helplessly. Dante and his guide through Hell, the ghost of the poet Virgil, observe from the left, while
a demonic angel watches over all.
