The coat of plates used larger internal plates to reinforce the torso before fully shaped breastplates became common.
The coat of plates is a transitional defence of the thirteenth and fourteenth centuries: iron plates riveted to the inside of a fabric or leather garment, worn over mail. From the outside it looks like a sleeveless coat studded with rivet heads; the armour is entirely hidden.
It marks the moment European armourers began putting rigid plate over the torso without abandoning mail. It is neither a mail garment nor a breastplate but a bridge between them, and its brief dominance maps almost exactly onto the century in which that transition happened.
It is also, unusually, an object known primarily from archaeology rather than from museums. The single most important source is a mass grave, and almost everything reliable about its construction comes from there.
The garment is a cover of stout linen, canvas or leather, inside which iron plates are laid in overlapping rows and riveted through. The rivet heads show on the outside in regular lines, and reading those lines is how the internal plate layout can be inferred from a painting or an effigy.
Plate arrangements vary widely. Some coats use a few large plates across the chest, others many smaller ones, and most combine sizes — larger over the chest where rigidity matters, smaller over the abdomen and flanks where the body must bend.
It fastens with straps and buckles, usually at the shoulders and down one side or the front, so it could be put on without help. That matters practically: an armour a man can don alone is worth more on campaign than one requiring a servant.
Its purpose is to defeat the thrust that mail could not. A rigid plate spreads a concentrated point across its whole surface, so the spike that would burst a mail ring instead meets an inch of iron backed by the wearer's ribs.
Worn over a hauberk, it produces a layered defence of textile, mail and plate, each covering the previous one's weakness. That combination is the standard equipment of the well-armed fourteenth-century man-at-arms and is what most figures in armour of that century are actually wearing.
The evidence for its battlefield use is unusually direct. The grave pits from the fighting at Visby on Gotland in 1361 contained around two dozen coats of plates, buried with the men who wore them, and the wounds on those bodies show exactly what the armour stopped and what it did not.
Its strength is that it adds rigid protection without sacrificing much movement. The plates are small enough and jointed enough by their fabric backing that the wearer can still bend, twist and mount a horse.
Its weakness is the gaps. Plates overlap but do not interlock, and a determined point can find the seams between them — which is why the armet-era solution was eventually a single shaped breastplate rather than an assembly of small pieces.
The cover is also a liability. Fabric and leather rot, straps break, and the rivets that hold everything together are the first thing to corrode — which is why nearly every surviving example is a set of loose plates and a stain where the garment was.
Coats of plates appear in the thirteenth century, becoming common from around the middle of it, as the answer to weapons increasingly designed to punch through mail rather than cut it.
They reach their widest use in the first half of the fourteenth century, the equipment of choice for a man-at-arms in the generation that fought at the Battle of Crécy in 1346 and the Battle of Poitiers in 1356.
They are superseded from the later fourteenth century by the solid breastplate, which does the same job better with fewer joints, and by the brigandine, which takes the same hidden-plate principle in the opposite direction — many smaller plates for more flexibility.
The Wisby finds dominate the surviving record so completely that the type is often described in their terms, which is a real hazard: an assemblage from one engagement, in one place, in one year, is now standing in for a century of European practice.
What those graves show is a range rather than a standard. Plate counts, sizes and arrangements differ substantially between individual coats, and some are clearly older equipment pressed into service by men who could afford nothing newer.
Elsewhere the object survives mainly as loose plates in museum collections, and as rivet patterns in art. The Metropolitan Museum of Art and the Royal Armouries hold examples, most reconstructed to some degree on modern backings.