How did Rome rise to dominate so much of the ancient world? Off the coast of Sicily, investigators discover traces of a crucial naval battle. Using divers, an underwater robot and a crane, they haul a long lost battleship relic to the surface. In Terracina, south of Rome, a team of archaeologists dig inside an ancient mountaintop temple, and in Carthage, Tunisia, clues reveal how one deadly rivalry tilted the scales of power in favour of Rome.