Fully-armoured medieval horses probably had a limited role in warfare, according to researchers.
David Jones and Emma Herbert-Davies, reporting in the EXARC Journal, came to that view after studying the effectiveness of mail armour in protecting horses against arrow shots.
They also set about assessing the circumstances in which such armour might play a useful role in combat.
Medieval European horse armour is largely known from illustrations and surviving documents. Although historical evidence points to the 13th century as the high point of its use in Europe, there are no known surviving examples that can be securely dated to that period.
In their absence, 14th-century mail, itself scarce, serves as a model.
There is only one known surviving example of a medieval mail crinet (neck defence for a horse), which is now in the Royal Armouries in Leeds, England. It is believed to have been made in the 14th century in Lombardy, Italy.
Since the protection given by mail armour is largely dependent on the thickness of the underlying padding, the researchers first estimated the maximum thickness of padding, comprising unbleached woven upholstery linen, that could be worn by the horse during cavalry operations.
Experimental tests were then conducted by shooting arrows with reproduction medieval bodkin points – uncomplicated square-section arrowheads – at reproduction mail over various thicknesses of woven linen fabric. The longbow used was made from Pacific yew.
The results showed big differences between individual shots under apparently identical conditions, largely because of variations in the armour on a millimetre scale.
Despite the wide variance between shots, it was clear that a wax coating on the arrowhead improved penetration.
With five layers of linen, wax increased the average penetration of 10 shots from 35.8mm to 44.8mm. With eight layers of linen, wax increased the average penetration of 10 shots from 24.8 to 45.0mm.
Even with 24 layers of linen under the mail, the waxed arrowhead pierced the final layer in eight out of 10 shots, with two shots reaching 12mm.
The pair concluded that it would not be feasible to attain complete protection against arrows by mail armour and linen padding while remaining within the carrying capacity of horses for day-long operations.
The combination of mail and 24 layers of linen would result in 56kg of horse armour, bringing the total load on the horse to 178kg, once allowing a total of 122kg for a 70kg rider, his weapons, armour and saddle.
This would have exceeded the sensible weight limit by 28kg for a typical warhorse of the era.
“In addition to the weight, the 19mm thickness of linen would add greatly to the thermal load on the horse, with a consequent risk of heat stress,” they said.
A realistic limit for all-day cavalry operations might be no more than three to eight layers of linen under the mail, which would have resulted in arrow wounds 20 to 60mm deep.
“Even if non-fatal, these wounds would have a detrimental effect and probably render the horse unmanageable,” they said.
A thin wax coating on arrowheads significantly enhanced penetration through mail and underlying linen, typically increasing the average depth by more than 20mm.
However, the protection given by armour mail and three or more layers of linen would be sufficient to negate the use of broad-bladed sharp-edged arrowheads that would otherwise inflict very severe wounds on unarmoured men and horses.
Mail armour in those circumstances might therefore make the difference between a wounded horse and a dead one, they said.
They concluded: “The fully-armoured medieval warhorse would probably have had a very limited role. The combined effect of weight and thermal loading meant that it could only perform effectively for relatively short periods.”
In engagements where remounts might be at hand, such as battles and tournaments, this would not have been a problem. However, for wide-ranging chevauchée type operations – a raiding method of medieval warfare that required sustained periods of speed and endurance – it would have proved counterproductive.
Evaluation of mail horse-armour. David Jones and Emma Herbert-Davies. EXARC Journal, https://exarc.net/ark:/88735/10624