What significant feature did the Romans introduce to anchor design to ensure it would set itself?

Answer

The stock

The Romans are credited with introducing the concept of the stock, a beam perpendicular to the shank, which helped ensure that one of the anchor's arms (the fluke) would dig into the seabed when dropped.

What significant feature did the Romans introduce to anchor design to ensure it would set itself?
inventionHistoryOriginmaritimeanchor