This summer, I’ve been re-watching A Game of Thrones—to the end in Season 8, which I simply couldn’t bear to do last time, knowing, from spoilers of various sorts, that a number of my favorite characters wouldn’t survive through the last episode. As I’ve watched, I’ve been intrigued by this—

For Daenerys and her forces, this is the equivalent of a modern attack aircraft, like these Fairchild Republic Thunderbolt IIs—

using fire in place of bombs and strafing.
I’ve wondered about that fire, however: where did it come from?
If we look at dragons when we first see them in Western literature in the Greco-Roman world, their danger seems to come not from flaming gasses, but from size and teeth and maybe just plain dragonicity.
[A footnote: the word dracon, in Greek, and draco, in Latin, are very vague terms, referring to scaly things from perhaps water snakes or whatever Herakles’ hydra is supposed to be

to beasts we might think of as dragons. For the purposes of thinking out loud about the subject, I’m going to assume that the creatures in these stories are all forms of what we would call dragons.]
A main source for early stories is the Library of the rather mysterious “Apollodorus”—so mysterious, in fact, that he’s now often called “Pseudo-Apollodorus”, although that seems a little unfair—who may have lived in the 1st or 2nd century AD. This is a huge collection of myth which records that the first human who appears to have encountered dragons in a hostile situation (at least for the human) was Minos (the Minotaur man).

Minos has his adventure in 3.3.1, where, in a complicated story of death and rebirth, Minos kills one dragon with a stone, only to have another dragon appear, who heals the first, whereupon they disappear from the story. The dragons, in fact, seem to have no interest in Minos and all that’s said of them suggests nothing of the fearsome, but rather of the magical.
Cadmus, the founder of Thebes, is the second to be involved with dragons, having dealt with one who had killed most of his men who had gone to a spring for water, in the Library, Book 3.4.1.

Cadmus kills the dragon, the text doesn’t say how, but there’s no more detail about the dragon than that it was a dragon and that it had slain Cadmus’ men.
Perhaps Apollodorus had left something out? There is a late commentary on the story in the so-called “Chiliades” (“Thousands”) of John Tzetzes (c1110-1180AD), a Byzantine literary man, which adds the details that there were two men sent, Deioleon and Seriphos, and that:
“….the dragon, the guardian of the spring, killed them both,
but Cadmus, with the throwing of stones, killed the dragon…”
(Chiliades, X.406-407)
But that’s all the description we get—just a dracon, albeit, in the Cadmus story, given to homicide.
When Eurystheus

(he’s the one cowering in the big jar)
demands that Herakles do two more labors, the first of the two is to fetch the Golden Apples of the Hesperides,

(by the Pre-Raphaelite painter Edward Burne-Jones, 1833-1898, the besty of William Morris),
which were guarded, in one version of the story ,by a deathless, hundred-headed dragon (Apollodorus, the Library, 2.5.11). Herakles kills the dragon (Apollodorus doesn’t say how, any more than he provides any details about the dragon).

Continuing through mythical history, we now arrive at Jason, who, in his quest to obtain the Golden Fleece, finds that the fleece is guarded, like the Golden Apples, by a dragon—this one both immortal (Apollodorus, The Library 1.9.16) and sleepless ( Apollonius, Argonautica 2.1209-10). When, in Apollonius’ (3rd century BC) Argonautica, Book 4, Jason actually confronts the dragon, it has an amazingly loud hiss (4.130-131 ) and huge jaws (4. 154-56 ), but is quickly subdued by the enchantress Medea, with a sung charm and a drug for his (now very sleepy) eyes (4.156-58) and, as ever, no fire.
Even in Ovid’s (43BC-17AD) retelling of the Jason story, in Book 7 of the Metamorphoses, the dragon is only described:
…linguis…tribus… et uncis
dentibus…
“with triple tongue and with curved teeth” (Ovid, Metamorphoses 7.150-151)
It’s interesting, however, that, in the Jason story, there is fire-breathing, just not reptilian. Before the King of Colchis, Aeetes, will deal with Jason’s request for the Fleece, he sets him a task:
1. he must yoke bronze-hoofed bulls

2. he must plow a field with them
3. he must sow dragon’s teeth

and then fight the warriors who spring up from the teeth.
As if all of this weren’t difficult enough, the bulls breathed fire. As Apollonius describes it:
“And they up to that time were raging exceedingly,
The pair of them breathing out turbulent flame of fire…” (Argonautica 3.326-7)
Bovine fireworks, but nothing from dragons—and yet, somewhere along the way between these early dragons and Beowulf,

something set off the reptiles and, from that moment on, dragons were flaming.

(from Peraldus’ Theological Miscellany—1st half 13th century—this image is from one of the medievalist Hana Videen’s websites and I recommend all of them. Start with: https://oldenglishwordhord.com/ which is ongoing, but there are also https://medievalandmodernbestiary.com/about/ and https://medievalcomicsblog.wordpress.com/ )
I have two suggestions for possible models for this change—and I’ll put “possible” in quotation marks to show just how tentative I think these are.
First, as early as Aristotle (384-322BC), there was the belief that salamanders could live in fire (Historia Animalium 5.19),

a fact repeated by Augustine (354-430AD), in Book XXI of his De Civitate Dei Contra Paganos, where he cites the example of a salamander’s survival in fire to suggest that the damned could burn for eternity and not be consumed:
“ut scripserunt qui naturas animalium curiosius indagarunt, salamandra in ignibus uiuit…”
“…as they have written who, curious, have investigated the qualities of animals: the salamander lives in fires…” (XXI.iv)
Imagine, then, a lizard-like creature, as we see in medieval illustrations—

associated with fire from as far back as the Greco-Roman world…
Second, there is a fire-spouting weapon which could also have served as a model/inspiration: Greek fire.

As early as the late 7th century AD, the Byzantines had not only invented a new and terrifying weapon, the compounding of which is still unknown, but guessed at,

but also a way to project that fire over a distance—almost as if were being breathed out.

(Here’s a short film clip which demonstrates just how frightening this weapon could be: https://www.youtube.com/watch?v=lPUgvYZ5UDk )
Think of it flying–certainly not something you could, like Cadmus, knock over with a stone.

Thanks, as ever, for reading.
Stay well,
Never say “Dracarys” unless you mean it,
And know that there’s always
MTCIDC
O
PS
Although I love science—especially the natural sciences—I’m certainly not a scientist, but does the explanation below seems oddly plausible to you?
“One possible way: Their metabolism is capable of creating a low-boiling flammable liquid (such as diethyl ether or pentane) and this substance is stored in sacs somewhere in the head. The dragon also has an enzyme that acts to ignite the stuff when in contact with air.
To breathe fire, the dragon pumps (by muscle action) some of this liquid out of its mouth; its own body heat evaporates it and the enzyme, sprayed out at the same time, sets it off.”
(Ian Campbell, BA in Natural Sciences, Cambridge, 1979—from Quora at: https://www.quora.com/When-did-people-start-to-depict-dragons-as-firebreathing-in-mythology-What-was-the-first-ever-fire-breathing-dragon-myth-in-history?share=1 )