stress for grip/torso/saddles during couched lancing

[Rasna]

Originally Posted by DanHoward

He just says "armour", he doesn't say what type.

Right.

Giving the context, probably it does refer to "mail" + "mail" or "mail" + "something else" (scale/lamellar/textile/leather).

[Donny Brook]

Originally Posted by Verjigorm

I doubt this. Various horse mounted peoples were described by contemporary records as being able to drive a lance through two armored men. Persian cavalry were alleged to tied their lances to tie their lances to their horses. For hundreds of years prior to the invention of stirrups, we have accounts of men on horses with long pointy sticks charging people, and sometimes, successfully.

My personal opinion is that Stirrups empowered both mounted archery, and mounted close combat. When you swing a sword, or throw a punch, you use the entirety of your body. With stirrups, you can "stand" in the saddle, almost like you were on solid ground. Without stirrups, you have to cling to the back of a horse with your thighs.

You may be right to doubt it, but at the same time, you certainly don't need the full force of a horse and rider to put a spear going 25kph through a human body or two. The particulars of the armor would make a difference though.

[DanHoward]

Originally Posted by Rasna

Right.

Giving the context, probably it does refer to "mail" + "mail" or "mail" + "something else" (scale/lamellar/textile/leather).

No, the context doesn't help tell us what kind of armour.

[Pursuivant]

Something that isn't emphasized enough in accounts of jousting/mounted spear use is the recovery after the strike. You have to hang onto the lance while somehow unsticking it from whatever you've just skewered, then bring it back into line and ready it again.

That bit of the job is entirely based on the rider's ST and skill.

Gadgets like pennants or lugs were sometimes added to keep the weapon from penetrating too deeply or overpenetrating. (After all, driving a sharp stick 6" into the human body is plenty deep enough to puncture any vital organ. No need to go any deeper.)

While a lancer could skewer multiple foes, they probably didn't want to if they wished to retain their weapon. After a trick like that the rider probably left the infantry-kabob behind and went for a secondary weapon like a melee weapon or bow (or pistols for lancers of later eras).

[Rasna]

Originally Posted by DanHoward

No, the context doesn't help tell us what kind of armour.

What types of armour we know they were in use among the Roman troops in the eastern portion of the Roman Empire during the campaign of Julianus against Shapur II (AD 363)?

Predominantly, mail for body armour and plate for helmets. Then scale. Then other things. So, in this case "double armour" is likely to be "mail + mail" or "mail + something else".

Note that the Ammianus Marcellinus description of a lance hit on charge being capable to pass through the foe's human body and then hit another foe which is positioned behind the first does not sound at all being a literary hyperbole like the "a mounted Frank is irresistible, able to bore his way through the walls of Babylon" written than Anna Comnena eight centuries afterwards. So it is plausible that, on occasion, strong cavalry charges with heavy lances were capable to pierce two layers of armour, then injurying or killing the wearer.