science

Polybolos

Polybolos is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polybolos rather than just read about it. In short: The polybolos (the name means "multi-thrower" in Greek) was an ancient Greek repeating ballista, reputedly invented by Dionysius of Alexandria (a 3rd-century BC Greek engineer at the Rhodes arsenal,) and used in antiquity. The polybolos was not a crossbow since it used a torsion mechanism, drawing its power from twisted sinew-bundles.

Key takeaways

Polybolos belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polybolos to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polybolos from memory before moving on to harder problems.

Reference excerpt

The polybolos (the name means "multi-thrower" in Greek) was an ancient Greek repeating ballista, reputedly invented by Dionysius of Alexandria (a 3rd-century BC Greek engineer at the Rhodes arsenal,) and used in antiquity. The polybolos was not a crossbow since it used a torsion mechanism, drawing its power from twisted sinew-bundles. However the earlier and similar oxybeles employed a tension crossbow mechanism, before it was abandoned in favor of torsion. Philo of Byzantium (c. 280 BC – c. 220 BC) encountered and described a weapon similar to the polybolos, a catapult that could fire again and again without a need for manual reloading. Philo left a detailed description of the gears that powered its chain drive (the oldest known application of such a mechanism) and that placed bolt after bolt into its firing slot.

Design The polybolos would have differed from an ordinary ballista in that it had a wooden hopper magazine, capable of holding several dozen bolts, that was positioned over the mensa (the cradle that holds the bolt prior to firing). The mechanism is unique in that it is driven by a flat-link chain connected to a windlass. The mensa itself was a sliding plank (similar to that on the gastraphetes) containing the claw latches used to pull back the drawstring and was attached to the chain link. When loading a new bolt and spanning the drawstring, the windlass is rotated counterclockwise by an operator standing on the left side of the weapon; this drives the mensa forward towards the bow string. At the very front, a metal lug triggers the latching claws into catching the drawstring. Once the string is held firm by the trigger mechanism, the windlass is then rotated clockwise; pulling the mensa back and drawing the bow string with it. At the same time, a round wooden pole in the bottom of the magazine is rotated via a spiral groove being driven by a rivet attached to the sliding mensa; dropping a single bolt from a carved notch in the rotating pole. With the drawstring pulled back and a bolt loaded on the mensa, the polybolos is ready to be fired. As the windlass is rotated further back to the very back end, the claws on the mensa meets another lug like the one that pushed the claws into catching the string. This one causes the claws to disengage the drawstring and automatically fires the loaded bolt. Upon the bolt being fired, the process is repeated. The repetition provides the weapon's name, in Greek πολυβόλος, "throwing many missiles", from πολύς (polys), "multiple, many" and -βόλος (-bolos) "thrower", in turn from βάλλω (ballo), "to throw, to hurl", literally a multithrower. A series of marks from ancient impacts on the walls of Pompeii, similar to those made by modern machine guns have been attributed to a polybolos operated by the troops of Roman commander Lucius Cornelius Sulla, who besieged the city in 89 BCE.

Popular culture In 2010, a MythBusters episode was dedicated to building and testing a replica, and concluded that its existence as a historical weapon was plausible. However, the machine MythBusters built was prone to breakdowns that had to be fixed multiple times.

See also Gastraphetes Repeating crossbow Rapid fire crossbow Chain gun Panjagan

References

Bibliography Duncan B. Campbell and Brian Delf, Greek and Roman Artillery 399 BC–AD 363, New Vanguard series 89, Osprey Publishing Ltd., Oxford 2003. ISBN 1 84176 634 8 Joseph Needham, Science and Civilization in China: Volume 5, Chemistry and Chemical Technology; Part 6, Military Technology: Missiles and Sieges, Cambridge University Press, Cambridge 1995. ISBN 978-0521327275, 052132727X

External links

The Repeating Catapult of Dionysius Reconstructed Polybolos in action Archived 2013-12-02 at the Wayback Machine (clip)

Illustrations

Worked examples

Example 1 — a first encounter with Polybolos

Start with the simplest possible case. Write down what Polybolos claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polybolos before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polybolos ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polybolos

In research: Polybolos appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polybolos in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polybolos is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ancient Greek artillery, Lost inventions, Projectile weapons, so understanding it makes those chapters shorter.
In everyday life: Look for Polybolos outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Polybolos in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polybolos means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Polybolos out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polybolos in simple terms?

Why does Polybolos matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polybolos?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polybolos.