Quetzalcoatlus was about the size of a giraffe, though there’s some controversy over how much it weighed and whether it could achieve powered flight. I’m guessing the larger dragons would be magic themselves – magic flight, magic fire breath. If the fire breath is chemical based then it would run out of fuel in short order. An animal that size would take an enormous amount of energy to fly for any length of time, so, magic.
A lot depends on how big it is.
Whales and mammoths have thick skin and fatty deposits but humans can take them down with spears and harpoons. Even if it has skin like plate armor the skin of the wings will be thin and should be damaged by missiles. Once the wing flap skin tears it can’t fly for awhile.
Could launch pots of chemicals at it, either caustic or sleep inducing (King Kong style). Not sure what the ancients had in terms of chemical know how but I’m sure they could cook up something nasty. The Greeks could launch Greek fire at it, maybe. Unless it’s that BS RPG stuff where dragons are immune to all fire attacks.
You could drop big rocks on it, best in a mountain/valley.
If you had enough people you could spread out groups of attackers so it can’t land anywhere for long. It would fly until it was exhausted, then you could converge. Not as effective in mountainous regions, or if it’s smart enough to see the trick and fly outside its territory.
Could have two teams. One drags it down with ropes, grapples, and nets. The other rushes in and stabs it with spears. High casualties, but it could get the job done if it’s not much bigger than 20-30 foot.
You could set a giant glue trap and bait it. I’m not actually sure if you can trap a large animal that way, but it’s worth a shot.
Another idea is to guard the waterways. It has to land to drink eventually. Hopefully you’re not in the land of a thousand lakes.
You can ignore realism just for the sake of a fantasy dragon, but in the interest of weight reduction a big flying animal probably wouldn’t have particularly thick or armored skin. And it’d probably have a gracile build. I think even really old societies could defend themselves from that. Massed atlatl fire would probably make it think twice.
Let’s consider it in these terms: How could a group of primitive agricultural screwheads successfully do battle with an armored attack chopper armed with incindiary weapons? That is, in effect, the situation. They have to get it while it is on the ground
We can pick up coins and gems and move them to where the dragon wants them. Opposable thumbs, baby! So we could move the target dragon’s treasure to any point of choosing for the hired hitdragon.
I don’t think this should work. While I was being ironic before when I suggested that dragons would be social and telepathic, dragons that collect treasure must have some means of collecting and moving treasure (otherwise, they would be unable to …).
Maybe a smaller dragon could be tempted to attack the resident dragon for its treasure if it could be convinced that we could offer sufficient assitance to make it workable. Intelligent, non-Chinese, mythologic dragons are almost always portrayed as avaricious.
After the dust settles, maybe we could kill the survivor? I like the ideas involving barrels of pitch- it’s hard to fly weighed down with glop, especially with pitch-befouled wings. The pitch may ignite if it flames.
You could also take advantage of intelligence + avarice; go for the long con!
Just a WAG, but maybe treasure hoarding dragons swallow the gold and precious stones and then regurgitate it back in their lairs. They are often portrayed as, literally, lying atop a mound of treasure rather than having it packed away in chests.
