Coat of plates

The coat of plates emerged because medieval warriors needed protection that mail armor could not provide against the increasingly powerful weapons of the 12th and 13th centuries. Mail excelled at stopping slashing attacks, but heavy blows from maces, war hammers, and crossbow bolts could crush bones and penetrate rings. The solution was to combine mail's flexibility with rigid plates riveted inside a cloth or leather garment, distributing impact force across wider areas and presenting harder surfaces to incoming weapons.

The coat of plates represents a transitional armor form—the bridge between pure mail and the full plate harness that would define late medieval warfare. Its introduction among European warriors occurred in the 1180s or 1220s, becoming well established by the 1250s. By the 1290s, it was nearly universal among heavy cavalry, and by the 1350s even infantry militias commonly wore some version of plated armor.

Construction involved riveting multiple overlapping iron plates to the inside of a fabric or leather covering. The plates varied in size and arrangement, with larger plates typically protecting the chest and smaller plates covering the sides and back where more flexibility was needed. The outer fabric concealed the armor's nature—opponents could not immediately assess its construction or coverage areas. Some coats displayed their rivets prominently; others hid them beneath cloth, presenting a deceptively simple appearance.

The coat's effectiveness became dramatically apparent at specific battles. German knights wearing coats of plates at the battles of Benevento (1266) and Tagliacozzo (1268) proved nearly invincible against French sword blows. The rigid plates distributed cutting force that would have severed mail links, and the underlying padding absorbed shock. Contemporary accounts describe opponents exhausting themselves striking armored knights with little effect.

Scandinavian sources provide detailed terminology. The Konungs skuggsjá (King's Mirror) from around 1250 calls it a 'Briost Bjorg.' The later Hirdskraa of the 1270s names it a 'plata' and specifies that warriors should wear it beneath their hauberk (mail shirt). This layering—plates under mail—provided maximum protection, with mail stopping cuts that might find gaps between plates, while plates distributed impacts that would bruise through mail alone.

Some historians speculate about possible Mongol influence, noting similarities to the khatanghu degel, a Mongolian armor type featuring scale or plate elements lined within fabric. Whether this represents direct technology transfer or convergent development remains debated, but contact between European and Asian military traditions during the Crusades and Mongol invasions certainly exposed both cultures to alternative armor concepts.

The coat of plates proved so effective that it drove its own obsolescence. After about 1340, armorers began combining the chest plates into single, articulated breastplates—essentially taking the coat's central protection and refining it into specialized components. By 1370, complete breastplates covering the entire torso had emerged. The coat of plates had demonstrated what rigid protection could achieve; the full plate harness represented its logical evolution, extending the principle to cover the entire body with articulated steel.