Common Errors (1): Archimedes’ Heat Ray

It is one of the most impressive movie scenes I have ever seen: how Archimedes set Roman warships afire with a burning mirror, in the famous Italian movie Cabiria (1914; scene starts at 20’24). The incident, which took place during the siege of Syracuse in 212 BCE, can be found in many history books and continues to amaze. Unfortunately, it can not be true.

Scene from Cabiria: Archimedes hexagonal mirror (top) sets a Roman ship (front) afire.

Scene from Cabiria: Archimedes' hexagonal mirror (top) sets a Roman ship (front) afire.

There are two arguments. In the first place, the laws of physics. On at least three occasions, people have tried to repeat the trick; they established that, if you use dozens of mirrors, you can indeed set fire to an object at a short distance (50-60 meter). The sources, however, refer to only one mirror or a couple of mirrors. Worse, the object must remain on the same place for some time, which is not very likely: the Roman galleys were subject to waves, winds, and swell. To really work, the mirror must have a diameter of at least eleven meters, which is larger than the largest telescope mirror ever made.

As a practical instrument, the weapon can, therefore, not exist, unless Archimedes could suspend the laws of nature. The story is pseudoscientific in its most elementary sense.

The second argument is that the famous incident is not recorded in our sources. Historians like Polybius, Livy, and Plutarch offer detailed descriptions of the siege of Syracuse and mention new weapons, but the heat ray is not among them. This is sufficient to send the story to the country of fairy tales.

But what are the origins of the story? Now, things become more complex.

The first to refer to Archimedes as firemaker appears to have been the satirical writer Lucian, who praises an engineer for having surpassed several legendary engineers, including Archimedes, who invented an instrument to set ships afire (Hippias 2). We know more about this from Lucian’s younger contemporary Galen, who offers an account of spontaneous combustion of houses, and adds that “this, they say, was how Archimedes set fire to the enemy ships by means of pyreia” (On Temperaments 3.2). Pyreia is usually translated as “firesticks”. Note that Lucian and Galen do not identify the enemy.

As far as I know, the first to refer to Archimedes using mirrors, is the Byzantine author Anthemius of Tralles (sixth century) in a book called On miraculous engines. On page 153 and 156 (ed.Westerman), he informs us that Archimedes’ secret weapon consisted of many small, flat mirrors. The Byzantine author Tzetzes (twelfth century) even offers a detailed description:

Archimedes constructed a kind of hexagonal mirror, and at an interval proportionate to the size of the mirror, he set similar small mirrors with four edges, moving by links and by a kind of hinge, and made the glass the centre of the sun’s beams … So after that, when the beams were reflected into this, a terrible kindling of flame arose upon the ships, and he reduced them to ashes a bow-shot off (Chiliades, 2.109-123).

This is the instrument shown in Cabiria, but the experiments have shown that it is too simple to do the job; Tzetzes cannot have used an authentic source.

There’s perhaps one author before Anthemius who may have referred to burning mirrors: the third-century historian Cassius Dio, but his account of the siege is lost. However, Tzetzes’ older contemporary Zonaras summarizes Dio’s History of the Roman Empire, and refers to the burning mirror. The problem is that Zonaras often introduces stories to his excerpt, and this may be one of these additions; worse, he also writes that this weapon was used in 514 by one Proclus, when he defended Constantinople against the ships of the Gothic adventurer Vitalianus (Annals 14.55).

Summa summarum: I think that Proclus’ experimental weapon, which must have been known to Anthemius, is the origin of the story. Alternatively, the story of Archimedes’ mirrors appears to have been invented in the age of Lucian, Galen, and Cassius Dio, about half a millennium after the siege of Syracuse.

This is not unique: think only of Pythagoras, who is never credited with the theorem that is now named after him, until the fourth century CE.

<Overview of Common Errors>


12 Responses to Common Errors (1): Archimedes’ Heat Ray

  1. […] Jona Lendering points out that the common story that Archimedes used mirrors to set fire to Roman galleys rests on, erm, no historical source earlier than half a millennium later.  He lists the data and concludes the whole story is a legend.  Very interesting indeed, and highlights the need to tabulate the data before evaluating it. Tags: Ancient legends. […]

  2. barcid says:

    Mr Lendering, in your opinion, do you think Hannibal Barca really melted holes through massive boulders in the Alps using fire and vinegar?

  3. rambambashi says:

    Why not? It was a common method.

  4. barcid says:

    Well I don’t know for sure, but I heard that vinegar only works on limestone and most boulders in the Alps are granite. Livy, if memory serves correctly, is the source, but he was writing long after the Second Punic War, and Polybius said nothing about it.

    Again, I’m not a chemist, and I don’t know what the boulders in the Alps are made of, I’m just relaying what I’ve heard.

  5. rambambashi says:

    Good point; I don’t know…

  6. barcid says:

    Just another one of those things about Hannibal that we’ll never know for sure, I suppose…

  7. Bill Thayer says:

    I just noticed (in a neglected part of my own website! a footnote of mine to Plutarch’s Life of Marcellus) that Athanasius Kircher debunks the story in 1645 already….

  8. brink1948 says:

    Please have a look at recent these conclusive technical tests by students of the prestigious Massachusetts Institute of Technology(MIT) made in cooperation with the team of the well-known Mythbusters.
    This was on instigation of Obama himself, see ref 2.
    This is much better than your “alpha” conjections on on the site. This is also on the idea of dissolving solid rock in vinegar: I’d like to see somemone do that.


  9. (1)
    For non-Dutch readers: the word “alpha” in the comment above is a reference to a colloquialism for scholar.

    The article you refer tp describes the conditions that would allow Archimedes’ weapon to work. It can be shown that the principle is sound. But that’s not at issue. The conditions are too rare to make the weapon effective. A ship needs to remain exactly in the focus, in spite of swell and surf, and the simple fact that it was moving to Syracuse. To assume that a Byzantine anecdote, just because something might work, refers to something that did work is a grave logical fallacy (the introduction of a secundum quid). And that is true for alpha’s and bêta’s, for scholars and scientist.. 😉

  10. Bill Thayer says:

    I think the sheer quantities of vinegar that would have to have been involved, and the undoubted fact that vinegar will only work on calcareous rock, put the Hannibal vinegar story in the same league as the Archimedes sunray tale.

    It’s just conceivable that both stories are partially true, but got wildly exaggerated. If for example one particular boulder was impeding the Carthaginian progress at some point; or if a sunray was focused on some critical rope or mooring or sail, which once destroyed would have wreaked havoc in the Roman fleet — well, we’d have the beginnings of a legend.

  11. brink1948 says:

    dear Jona,

    Very very pleased to see a reply, after trying for weeks to get a comment on the site. Due to all attempts my latest reply, featuring at the site now, is both is rudimentary and rude.
    As for the test, you are right. The MIT team used a non-moving target and this was not the final answer.
    In the latest test, personally asked for by Obama, the target was a real boat at sea and an array of 500 mirrors was used. Temperatures got nowhere to the ignition point of the sail that was used as the target. The conclusion was, in their words:
    myth busted!

    Am embarrassed you had to correct me with respect to “alpha” man, with its different meaning in Dutch (German) and English.

    Harry ten Brink

  12. brink1948 says:

    Reply to Bill

    The vinegar might indeed dissolve carbonate, when it is as brittle as chalk. A simple hammer would do a better job then.

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