Saturday, March 7, 2020

Bret Devereaux's The Siege of Gondor

Bret Devereaux is a lecturer in history at UNC and specializes in ancient (Roman era) history, and I very much enjoyed his recent multi-part essay on the military history of the Siege of Gondor in The Lord of the Rings

The whole thing is marvelous. I am certain that, had I been lucky enough to have a history professor as entertaining as this, I should never have chosen mathematics (well, I'm sure I would have ended up in maths anyway, but I wouldn't have dreaded my history classes anywhere nearly as much).

  • Part I: Professionals Talk Logistics
    That may seem a touch early to start a review of the siege, but there are two points to this, both of which are historically illuminating. What we are watching at this stage is what is called operations – the coordinated movement of large bodies of troops to their objective. Operations is the level of analysis between tactics (how do I fight when I get there?) and strategy (why am I fighting at all?). And its worth asking, before proceeding any further: what is Sauron’s overall plan and does it make sense?
  • Part II: These Beacons are Liiiiiiit
    You may be waiting for me to now say that the Beacons of Gondor is a silly, a-historical thing that could never happen. Nope. Not only is this system plausible, it existed, on a similar scale, in the 9th century Byzantine (read: Eastern Roman) Empire. The system stretched more than 400 miles from the frontier to Constantinople, and consisted of fire signals set on high ground at intervals of 30 to 60 miles.

    This was particularly important because of the way the Byzantine Empire’s army was organized into themata or themes. Each theme was a combined military and civil administrative district, with its own small field army that could respond to local raids – however a theme’s army would be insufficient to respond to a major invasion. In the event of a large attack, the beacons rippling back to the capital would bring the tagmata, the main imperial field army, which tended to stay wherever the emperor was (to discourage rebellion in the themes). The tagmata could then roll out to confront the invasion, picking up theme forces as it moved (forces which – because of the beacons – would already be ready). It was an effective system and despite the Byzantine reputation for decline, the period from the 9th century to the 11th century was a period of Byzantine reconquest and consolidation (until the Battle of Manzikert in 1071).

  • Part III: Having Fun Storming the City
    The design of the orc catapults, on the other hand…oof. This is not a great design. On first viewing, I thought these were torsion catapults (like the Roman onager – a late Roman single-armed torsion siege engine), because in the wide shots where the catapult is presumably pure CGI, the firing arm snaps very quickly forward when fired. Counterweight catapults do not ‘snap’ like this, because the counterweight can only accelerate as fast as the constant acceleration due to gravity (9.76 m/s). Nevertheless, in the close shots, it is clear that these are counterweight catapults, with the large stone counterweights clearly visible on the far end of the arm. So what’s wrong?
  • Part IV: The Cavalry Arrives
    They are, however, in the wrong formation. For cavalry, this formation is very deep. The front block looks to be about 12-14 horses deep, and the rear block seems to be about as large, making the entire formation c. 24 x 250 (we were told they had 6,000 horses, you will recall). This is a very deep cavalry formation (presumably so it would neatly fill the screen), which is mostly a problem because of the size of the enemy force. Attacking with such a purposefully narrow front means that the Rohirrim will be enveloping themselves on contact. This is particularly dangerous for cavalry because the feint is so important for cavalry tactics.
  • Part V: Just Flailing About Flails
    Now we see one unfortunate Gondorian soldier tossed what looks like more than 20ft in the air (he is well over the heads of the trolls) – how much energy does it take to do that? In our own simplified high school physics sort of way, we can figure this out, very roughly. The energy required to lift a thing is equal to its potential energy after being lifted, which is equal to it’s mass, times the gravitational constant, times its height, in this case 6,576J (110kg * 9.8m/s^s * 6.1m); the hit must have imparted at least this much energy (more, in fact – we haven’t accounted for friction or air resistance). Since the club is still moving very fast, we might assume it retains something like half of the energy of impact (again, this is almost certainly a low-ball figure), so the initial kinetic energy of the club the moment before impact is c. 13,000J – the equivalent energy to a bit more than 3 grams of TNT.

    As noted above, we might expect a trollish warhammer to be around 13.5kg tops – so how fast does the troll have to get it moving to launch a man? Kinetic energy is equal to 1/2 mass times velocity squared, so (13,000J = 1/2 * (13.5kg) * (v^2)), solve for ‘v’ (velocity in meters per second). 43.9m/s (98mph). That is very fast – for comparison, professional golfers, using long and quite light-weight clubs cap out under 130mph for the highest speed of the head of the club in their swing – and golf clubs are made to maximize head speed. And we have made a lot of favorable assumptions for the troll (for instance, a lot of the energy of impact is going to be absorbed by the body as it crumples or recoil into the hand of the troll; we also assumed the entire mass of the hammer is up at the point, which it isn’t). I think it is fairly safe to say that a troll’s one-handed swing is probably not sufficient to get the impact surface of a club or hammer moving at 100mph.

  • Part VI: Black Sails and Gleaming Banners
    Tolkien’s vision of war is more nuanced, shaped by personal experience. War machines matter, but chiefly as a means of degrading the will of the enemy. The great contest is not between engines or weapons, but between the dread of Mordor and the courage of men. Catapults, towers and rams are merely the means that Mordor uses to deliver its terror. I have tried to flag instances of this in the book notes throughout this series, how close attention Tolkien pays to despair, dread and fear on both sides. The power of the Witch King’s catapults was that “the valour of the City was beaten down” (RotK, 108). But Jackson shows us not the despair of the soldiers but the shattering of buildings. When the Rohirrim arrive, the key thing we are told is that “the hosts of Mordor wailed, and terror took them” (RotK, 124). By contrast, Jackson opts to show us not the wailing of orcs, but the impact of horses.