Lately, I have heard the claim that medieval armor was actually dangerous to the knight wearing it since it could get extremely hot inside the armor so that heat exhaustion and heat strokes were a true risk to the knight`s life. That got me thinking. Did medieval armor really get so hot that it could endanger the life of its bearer?
Heat exhaustion and heat strokes could occur when knights wore full suits of plate armor, not because the sun heated up the armor, but because the plates locked in the knights` body heat. When knights wore chainmail, then they didn`t suffer from overheating since the wind could go through the rings of the armor and cool the knight down.
Let`s take a closer look!
The belief that knights in full armor regularly suffered from heat strokes and heat exhaustion probably comes from medieval sources from the First Crusade.
It actually seems like heat strokes and heat exhaustion occurred among the crusaders during the First Crusade. However, that probably had more to do with the fact that the knights, who fought in the crusade, mainly came from the much cooler central and western Europe (or even England). So they were simply not used to the climate and the temperatures of the Holy Land. That, combined with exhaustion and dehydration was a potentially dangerous mixture.
But as long as these knights remained in Europe, they most likely never had problems with heat exhaustion or heat strokes.
The reason why knights were not really at risk of overheating in their armor is the armor itself. Unlike in the Late Middle Ages, the knights in the Early and High Middle Ages used Mail armor to protect themselves. Since mail armor (commonly referred to as chainmail) consists of thousands of individual rings that are linked together, the body heat can not accumulate under the armor. Instead, the wind can go through the chainmail and cool the knight.
Aside from the construction of the chainmail itself, here you can find out more about how chainmail was produced, it was also helpful that the armor was not worn on the skin. While padding was optional underneath the chainmail, every knight wore linen undergarments under his armor.
That had two big advantages.
First, even when the metal armor got hot it did not have direct skin contact so it could not burn the knight. Additionally, the linen undergarments that a knight wore under his armor soaked up the knight`s sweat. So when the wind went through the rings of the Hauberk (shirt of chainmail), then the sweat in the linen undergarments evaporated and cooled the knight down.
So heat exhaustion and heat strokes were no risk to knights wearing chainmail as long as they remained in the cooler climate of Western and Northern Europe.
However, the same can not be said for Plate armor.
Plate armor slowly came up in the Late Middle Ages and it seems like at the end of the Middle Ages most combatants would wear more or less complete plate armor.
A full suit of plate armor basically surrounded the entire body with metal plates. That offered an extremely high level of protection (although there were still 2 ways to kill a knight in full plate armor), but it had one major disadvantage.
Unlike chainmail, the solid metal plates that enclosed the entire body kept the body heat beneath the plate armor and prevented the wind from cooling down the knight. So when the knight fought, then the body heat accumulated beneath his armor and could actually lead to heat exhaustion!
So yes: Heat exhaustion and heat strokes could occur when a knight wore a full suit of plate armor, but not because of the sun shining on the armor. Instead, the plates stopped the body heat of the knight from getting out, which could cause overheating.
So the risk that a knight in chainmail overheated in his armor was extremely low as long as he was fighting in the mild temperatures of Europe.
And yet there is the idea that the crusaders invented surcoats to prevent overheating by blocking the sun from shining on their armor. But that was not the case!
As stated above, the sun shining on medieval armor is not responsible for heating up the knight inside the suit of armor. Instead, the body heat of the knight is the true risk for overheating in armor when that body heat is encaptured beneath the armor (for example by plate armor).
The reason why a surcoat of cloth was worn over armor had nothing to do with the risk of the knight overheating in his armor when the sun shined onto the metal. Instead, covering the metal armor with cloth had the purpose of preventing the metal from heating up. During the first crusade, knights usually didn`t wear full suits of chainmail. Instead, many wore shirts of mail (Hauberks). But when the Hauberk was exposed to the sun, then the metal heated up. And when the knight accidentally touched the hot metal with an uncovered body part (like his hands), he burned himself.
Another effect of these surcoats was that knights in full armor were able to identify themselves and tell apart friends and foes on the battlefield. That became especially urgent when the Great helmet, a helmet that covered the entire face and that was usually worn over another helmet, was developed.
I hope you enjoyed our trip to the Middle Ages. Do you want to find out more about medieval armor? Then I would like to recommend you my article here, where I talk about how knights prevented their armor from rusting.
Take care of yourself because you deserve it. You really do.
Until next time
David S. Bachrach: Warfare in Tenth-Century Germany (Woodbridge 2012).
Malte Prietzel: Krieg im Mittelalter (Darmstadt 2006).
Alan Williams: The knight and the blast furnace (2003).