Porphyrios (Greek: Πορφύριος) was a large whale that harassed and sank ships in the waters near Constantinople in the sixth century. Active for over fifty years, Porphyrios caused great concern for Byzantine seafarers. Emperor Justinian I (r. 527–565) made it an important matter to capture it, though he could not come up with a way to do so. Porphyrios eventually met its end when it beached itself near the mouth of the Black Sea and was attacked and cut into pieces by a mob of locals.