Horse brass

A modern souvenir horse brass featuring Gloucester Cathedral
Horse harnessed with brasses
5th-century BC Celtic phalera from a chariot burial in Gaul

A horse brass is a brass plaque used for the decoration of horse harness gear, especially for shire and parade horses. They became especially popular in England from the mid-19th century until their general decline alongside the use of the draft horse, and remain collectors items today.

Phalera is the archaeological term for equivalent disks, which were popular in Iron Age Europe, including Ancient Rome.