The pilum has a legendary reputation for bending and breaking upon impact when thrown (some of it true some of it exaggerated)
however how well could it hold up to thrusting, especially perhaps thrusting at a shield or something harder than bare flesh.

im aware of 2 things
1 marius changed the design of the pilum head to make it more prone to breaking

but it also seems that roman manuals show pila raised and presented to the enemy as spears. as well as their impromptu use at the battle of carrae against the parthians

Short answer, "We don't know", and "It varied." How's that for a cop-out! Variations of the pilum were used for about a thousand years. Some were thick and heavy and could probably punch holes in buildings without a care. Others were scary thin and you really wouldn't want to do anything but chuck them.

Of course, bending isn't really "breaking", it just puts it out of action until you have time to straighten it out. And of course if it's already been bent a straightened a few times it could just break. I've straightened out plenty of pila in my time, but one really nice hand-forged one came back from a throw without it's point. (Not being a smith, I have since ground a new point into the remaining shank.) Modern mild steel isn't really like ancient wrought iron, though, so I'd hesitate to present any of that as scientific evidence!

There are a few modern experts who claim the whole bending thing is a myth, but Plutarch and Caesar both discuss it, and even state that it was desirable, so it clearly did happen. That said, the only pila that survive from the time of Marius have tangs with flanges that wrap around the wooden shaft, so even with only one rivet there is not going to be much swiveling or flopping of the shank! The whole description of him replacing one of the rivets with a wood peg therefore leaves us scratching our heads a bit, but it doesn't seem like the kind of thing that someone could just make up out of thin air.

Matthew

Right, I should have been clearer that I assume there could very well be some sort of lateral or twisting movement in a target when I hit it. Doesn't matter for a javelin or a regular spear (unless it gets extreme), but might bend a pilum that you are thrusting with.

Matthew

" because some famous figure "
Caesar isn't famous in the same way that Miley Cyrus is. He wrote a first hand account of his military invasion of Gaul and was a pre-eminent military figure in Ancient Rome. Unless he is directly contradicted by archaeology or other contemporary sources we should be confident in the veracity of his writings.
It is very hard to see what Caesar would gain from making up lies about how a mundane piece of military hardware worked.

Only a minority of ancient writers who write about the pilum mention bending. (Arrian mentions bending when used as thrusting weapon [1].) Penetration of armour and shields is mentioned more often. But why would one doubt Caesar on the pilum? There are other writers who mention bending, and it's supported by experimental archaeology, and by the performance of similar weapons.

It's true that much ancient writing that has come down to us is propaganda, and to just assume it all to be true is unwise. But, as mentioned above, technical details about well-known technology are unlikely to be propagandic claims. Polybius' comment on the bendiness of Celtic swords might be propaganda, but it's more likely to be error (possibly reflecting common opinion about barbarians). Which is why it's important that other writers and experiment support Caesar (as mentioned above). It isn't blind acceptance of Caesar as a source of truth. (We know that his Commentarii de Bello Civili is biased, but there's still plenty of correct and probably accurate stuff in it - useful history can still be done based on propaganda.)

Propaganda in ancient military writing isn't the problem for this kind of thing; it's that so few writers bother giving technical details. The lack of detail isn't surprising - how many modern newspaper articles about battles give technical details of the weapons?

[1] http://members.tripod.com/~S_van_Dorst/Ancien...taxis.html

A 2004 metallographic study of two early 2nd c. BC Roman pila found that the iron shanks between the shaft and the tips were incredibly soft: under 100 HV. It's clear that they were, as the written sources claim, designed to bend easily (and be easily straightened, once the battle was over, without snapping).

The points were almost twice as hard as the shanks.

Dimitrij KMETIČ, Jana HORVAT and Franc VODOPIVEC, 'Metallographic examinations of the Roman Republican weapons
from the hoard from Grad near Šmihel,' Arheološki vestnik 55 (2004): 291-312.

Hardness below 100HV just means that it's wrought iron. These aren't made of one piece of steel - a steel point is welded to a wrought iron shank.

I think it's more a matter of, rather than being designed to bend, the makers don't care if they bend after hitting a target. The design is (a) very good for armour and shield pierced, because of the long narrow shank, and (b) relatively cheap, since wrought iron rather than steel is used for the shank. Since there is a long narrow wrought iron shank, it will bend easily when subject to sideways forces (such as its own weight) after hitting a target.

Long-shanked spears that are not designed to bend will bend in this way. (As people throwing Cold Steel's version of a long-shanked East African spear into trees have found out.)