I'm reading Adrian Goldsworthy's Caesar: Life of a Colossus, and he mentions that contrary to popular belief the Roman pilum were not designed to bend upon impact. Before reading that, I was always told that the pilum was meant to bend upon impact, making it impossible for an enemy to throw back and a huge encumbrance on shields it had struck. What's the deal? Is the idea of the bending pilum a bunch of hot air?
Hello there! According to M. C. Bishop and J. C. N. Coulston's Roman Military Equipment From the Punic Wars to the Fall of Rome, 2nd ed. (Oxford: Oxbow Books, 2006):
It is often said of the pilum that it was designed to bend upon impact, thus rendering it incapable of instant re-use, but this is only one side of the story. This was not a function of the pilum, merely a useful consequence of its design. The pilum existed as a close-range javelin that used weight, as opposed to velocity, to provide its penetrative power. Moreover, careful consideration of the most common form suggests that it was designed as an armour-piercing missile, a fact witnessed by the pyramidal bodkin-head (a feature that medieval armour-piercing missiles, such as the crossbow quarrel and the English longbow arrow, were to exploit). As such, its prime function was firstly to pierce an enemy shield and then, carried by its own impetus (and with the narrow shank continuing unobstructed behind the larger head), assail the body of the enemy. Thus the long iron shank did not exist just to bend, but to provide the reach for the weapon between punching a hole in the shield and striking the bearer. Modern experiments with reconstruction weapons have shown the bodkin head capable of piercing 30mm of pine wood, or 20 mm of ply, when throw from a distance of 5 m, and that a barbed head was far less effective.
Nevertheless, it was characteristic of the pilum that the shank could suffer partial failure upon impact, disabling the weapon [due to its form]... Again, modern experiments in throwing pila have succeeded in reproducing the sort of bending seen on the shanks of excavated samples. (51-2)
Raffaele D'Amato's Arms and Armour of the Imperial Roman Soldier: From Marius to Commodus, 112 BC-AD 192 (London: Frontline Books, 2009) says something similar:
The pilum was a close-range javelin, consisting of a wooden shaft around 1 m long in which was inserted or to which was attached a long thin metallic shank of approximately the same length. Its penetrative power was determined by its weight. It was capable of wounding an enemy, but if the pilum, after piercing the shield, did not wound the enemy, it would have been broken by the impact at the junction of the iron shank and the wooden shaft, so that the opponent could not employ it again. The bent pilum stuck into the shield and could not be drawn out, so that the burdened shield was unserviceable and the enemy exposed to the slashing blows of the terrible legionary sword, the gladius. (6)
In his description of the Republican Roman army, Polybius mentions that the javelins of the velites bent on impact and were thus rendered unusable to the enemy (6.22.4). Caesar himself explains at one point in his commentaries that "when the iron [shank] had bent itself, [the enemies] were neither able to extract it nor, with their left hands impeded, fight with sufficient ability" (cum ferrum se inflexisset, neque evellere neque sinistra impedita satis commode pugnare poterant, Gallic Wars 1.25.4). Since Goldsworthy is an expert on Roman military matters, I assume he means that the pilum was not specifically designed to bend on impact (à la Bishop and Coulston), even though that's how it played out in practice; it's been several years since I've read his biography of Caesar, so correct me if I'm wrong. I hope you find this helpful! :D
Huh, that's curious. I had never heard of that either, the closest I've gotten to that is Gregory Daly's Cannae: The Experience of Battle in the Second Punic War where he says that the "narrow shank [of the pilum] would often bend on impact, ensuring the enemy would not throw the weapon back" (p.64-65).
However, a quick Google-search found this explanation, which says that Marius invented the bending pilum. Going back to the source (The Genesis of Rome's Military Equipment," by S. McCartney; The Classical Weekly, Vol. 6, No. 10 (Dec. 21, 1912), p.76), it says that Marius replaced the iron pins, that were joining the metal end with the wooden end, with wooden ones that would break on impact. It also says that Caesar accomplished the same by using soft iron.
Fun fact of the day I suppose. :)