Why did it happen in the 14th century, when the blast furnace was invented much earlier? Can someone explain, how medieval blacksmiths figured it out? What discovery enabled them to create plate armors?

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    Are you sure it was metallurgic advancements and not military necessity? You might want to rephrase to reflect that. I thought this transition was necessitated by advancements and prevalence of firearms. Combine this with the emergence of professional or mercenary armies, as opposed to prior levy armies. Commented Dec 27, 2017 at 19:54
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    Because it would have been expensive and not needed? I don't think you had massed crossbows or firearms in the 11th, and longbows would be impractical for most kingdoms. 11th century also had peasant levies ie poorly armed and untrained mobs. In the 14th and 15th you start to see large mercenary armies and an emerging professional soldier. Commented Dec 27, 2017 at 20:06
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    @Jotunn It took a long time for well designed, flexible plate armour to appear. But that's not metallurgy though. Also, it was extremely expensive - even the nobility did not have unlimited money.
    – Semaphore
    Commented Dec 27, 2017 at 20:45
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    So the only reason people didn't use plate armor was because it was expensive and wasn't needed against spears, axes, arrows and swords? And I don't think I wouldn't want to wear an armor, that renders almost all projectiles and weapons ineffective. There are also many videos where is shown that a full plate armor is not as immobile as people tend to believe.
    – Jotunn
    Commented Dec 27, 2017 at 21:41
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    @Jotunn Later plate armour did get much more flexible, but early ones were very burdensome to wear. Plate armour gave great protection but not invulnerability, so it was a significant tactical handicap. The French had plate armour at Agincourt and look how much good it did them against English longbows (it didn't). Production was a problem, but cost-effectiveness would've been the main constraint.
    – Semaphore
    Commented Dec 27, 2017 at 21:52

1 Answer 1


The emergence of late medieval full plate armour wasn't really prompted by any specific discovery or advancement in metallurgical tech. Partial plate armour, in principle, can be traced all the way back to Classical Antiquity, such as the Greek muscle cuirass later Roman lorica segmentata.

Rather, the most critical development was the appearance of larger bloomeries. It was no coincidence that plate armour began in North Italy shortly after such bloomeries appeared there - they made it possible to produce sufficiently large steel plates in one piece.

The suit of armour of large articulated plates first appears in 14th century Italy, followed later by Germany and the rest of Europe. This was a result of bloomeries having grown large enough to produce metal plates of the required size.

Williams, Alan. "The Metallurgy of Medieval European Armour." Proceedings of the Forum of the 4th International Conference on the Beginning of the Use of Metals and Alloys. Shimane, Japan, 1996.

The problem before this was that you need quite a sizeable amount of steel, about 10kg, for a breastplate. Prior to the late 13th century or so, European bloomeries were generally not large enough to produce so much steel in a single chunk. To make a steel breastplate then, you'd have to weld two or more separate plates together, which compromised its protective value despite an enormous price tag.

A plate of armour which weighs between 2.5 and 4.5 kg will pose new problems lo the producers. Billets of metal of 10kg or more may be needed to make such a plate

Williams, Alan R. The Knight and the Blast Furnace: A History of the Metallurgy of Armour in the Middle Ages & the Early Modern Period. Brill, 2003.

A significant factor behind the rise of larger bloomeries was that Late Medieval Europe began harnessing the power of rivers - using waterwheels to power furnace bellows enabled larger blooms of steel to be produced.

Once decent full plate armour became feasible to create, the main obstacle to adoption - aside from a lack of need early on - was simple economics. A full set of plate armour was extremely labour intensive to forge, and consequently very expensive. Keep in mind, even the Romans had to abandon the lorica segmentata after the Crisis of the Third Century rendered it economically and logistically unsustainable. No military in medieval Europe could rival the Roman Empire's resources.

By the 14th century, however, smiths had begun using watermills to driver hammers for shaping the steel, greatly reduced the labour required.

Water-power enabled smiths to increase their output. Bellows driven by a waterwheel could produce a continuous powerful draught from a free energy source, so it was at last possible to enlarge the size of the furnace and the bloom thus produced. Water-powered hammers were also heavy enough to fashion the larger blooms.

Blair, John, W. John Blair, and Nigel Ramsay, eds. English Medieval Industries: Craftsmen, Techniques, Products. A&C Black, 1991.

It was the newfound relative affordability of plate armour, combined with improved designs reducing its tactical downsides, that ultimately enabled its adoption. The full plate armour reached its peak about the same time advancements in projectile weaponry began to render it obsolete, however.

  • I thought it was because of crossbows. While mail armor can't stop arrows from a crossbows, plate armor is more likely to do it
    – Mandrill
    Commented Dec 28, 2017 at 1:36
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    @Mandrill The need for protection drove the adoption of plate armour, but it doesn't enable plate armour to be created, which I think is what the question is asking about.
    – Semaphore
    Commented Dec 28, 2017 at 7:19
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    +1. The increased need for protection made the cost of plate armor worth paying (standard arms race in play). Increased production volume of plate armor allowed improvements in technology, which drove costs lower, and adoption wider (standard market forces in play). Commented Dec 28, 2017 at 15:52
  • Remember that armor did not evolve from chainmail to plate directly but through various transitional phases (at least in Europe). You can check out 'coat of plates' and brigandine armor on wikipedia. Commented Dec 28, 2017 at 19:30

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