In the second century, the Greco-Roman writer Oppian described men in rowboats thrusting harpoons into a “sea monster,� which is then roped and towed to shore.

At the time, the Romans had a successful fishing industry in the Strait of Gibraltar, the western waterway to the Mediterranean world. Historians sometimes say Roman fishing at this bottleneck included whaling, but other than Oppian’s poem and other indirect clues, there was no evidence.

A paper published Wednesday in The Royal