Roman onion-knob brooches were predominantly made of brass or bronze, with some examples being gilded or decorated with enamel. Precious metals such as silver or gold were used less frequently. Since these brooches served as military badges of rank or status worn by soldiers and officials, the material provided direct information about social status: Expensive versions made of precious metal were often personally awarded by the emperor as a special distinction or gift, thus signifying high rank and particular honor within the imperial sphere.