Severo worked nearly his entire career in Padua, a university city where patrons' appreciation for the classical past fueled demand for small-scale works like this one. It was probably loosely inspired by the Greek myth of Perseus, who rescued the beautiful Andromeda from the rock where she had been chained by a sea monster. Here, it is the god of the sea who has vanquished the sea monster, a few links of the chain by which he had tethered the beast still surviving in his left hand. The reworking of classical themes was a specialty of Severo's, who had probably the largest bronze workshop in Padua. In Neptune on a Sea Monster, some elements, including the monster's gaping mouth, seem to have been adapted from an engraving by another, earlier, northern Italian artist deeply inspired by antiquity, Andrea Mantegna.
Neptune's carefully modeled, youthful body reveals the sculptor's command of anatomy and celebrates the god's eternal youth. His face, meanwhile, with deeply curling hair and beard, is that of an older man, who is more aware of the burdens of the world; this is a more common representation of the sea god. The head shows Severo's meticulous craftsmanship to advantage, as does the body of the sea monster, whose scales contrast with Neptune's smooth skin, and whose doggish ears and flippered paws show Severo's imaginative fantasy.