Soldiers who wore lorica hamatas (mail shirts) would add extra protection to their shoulders. They placed a U-shaped collar of leather or mail called "doublings" over their shoulders and attached the ends to their mail with four rivets. At the front, the ends were secured with a cord (later, with a metal hook). Although centurions wore lorica hamatas from the early Republic until the fall of Rome, doublings went out of fashion toward the end of the 1st century A.D.
Our centurion doublings are made of thick leather and brass plates that match our hammered brass Roman helmet with crest and centurion belt (both sold separately).