D&D 5E How many (ancient) dragons would it take to destroy a (dwarven) city?

[Mercurius]

So here's the scenario: There was a great dwarven city of approximately 50,000 within a mountain that was, a hundred years ago, utterly destroyed by a dragon (or two or three). Two-thirds of the population was killed, and the rest scattered widely. This city was the crown jewel of Dwarven civilization, after which it fractured and fell apart. It was a place of great craft and power - perhaps the greatest Dwarven city the world has ever known, well fortified and defended - perhaps with a strong army of 5,000 and a militia that doubled that number.

So my question is this: How many ancient, or at least very old and powerful, dragons would it take to destroy such a city? In what scenario could a single ancient dragon, or pair of dragons, destroy such a city? Or would it simply require many such dragons?

I'm trying to justify just two dragons doing the deed - an ancient female red and her younger but still rather old (and thus technically "ancient") blue consort. I'm imagining that while the blue took out the mithril golem guardians, the red figured out the flaw in the city's defenses (perhaps through treachery) and was able to collapse a cavern filled with most of the city's population. Or something like that.

Any thoughts, ideas, misgivings or fears?

 

[KarinsDad]

One dragon required. Attacks at night. If it runs into heavy resistance, it can hole up.

An ancient red dragon has AC 22 and Frightful Presence. Nobody could get near her in smaller areas and those that do couldn't hit her.

The dwarven heroes could manage it, but not normal low level fighter types. They would die by the hundreds with her breath weapon. The trick is to not allow 10,000 soldiers to fight her with bows all at the same time, rather she has to control the setting by getting into smaller areas (like 50 feet x 40 feet) where she cannot be overwhelmed with ranged attacks.

Also, nothing stops dragons from using magic items (like wands or staves). And my personal house rule for dragons is that they get 2x Charisma number of spells (I think that the rule in the MM is kind of weak). Dragons should be the ultimate foes of the D&D world in my view.

 

[Astrosicebear]

Just 1, if its name was Smaug.

 

[Mercurius]

One dragon required. Attacks at night. If it runs into heavy resistance, it can hole up.

An ancient red dragon has AC 22 and Frightful Presence. Nobody could get near her in smaller areas and those that do couldn't hit her.

The dwarven heroes could manage it, but not normal low level fighter types. They would die by the hundreds with her breath weapon. The trick is to not allow 10,000 soldiers to fight her with bows all at the same time, rather she has to control the setting by getting into smaller areas (like 50 feet x 40 feet) where she cannot be overwhelmed with ranged attacks.

Also, nothing stops dragons from using magic items (like wands or staves). And my personal house rule for dragons is that they get 2x Charisma number of spells (I think that the rule in the MM is kind of weak). Dragons should be the ultimate foes of the D&D world in my view.

Good stuff, thanks. Yeah, I think I can stick with my initial back-story - I just wanted to make sure it wasn't too far-fetched. I might even have it that the red did the deed herself, the the blue came later and courted her (the reason I want both is that eventually I hope to have the PCs take the city back, but they'll fight and theoretically defeat the blue, thinking that it is the dragon, and then find that it was merely the consort for a larger, older, more powerful red).

But yeah, I agree that ancient dragons should be, if not the most powerful monster in a D&D world, up there with the others. As it stands I'm guessing that a tarrasque would defeat an ancient red...hmm, that's almost thread-worthy.

 

[Dausuul]

So here's the scenario: There was a great dwarven city of approximately 50,000 within a mountain that was, a hundred years ago, utterly destroyed by a dragon (or two or three). Two-thirds of the population was killed, and the rest scattered widely. This city was the crown jewel of Dwarven civilization, after which it fractured and fell apart. It was a place of great craft and power - perhaps the greatest Dwarven city the world has ever known, well fortified and defended - perhaps with a strong army of 5,000 and a militia that doubled that number.

So my question is this: How many ancient, or at least very old and powerful, dragons would it take to destroy such a city? In what scenario could a single ancient dragon, or pair of dragons, destroy such a city? Or would it simply require many such dragons?

I'm trying to justify just two dragons doing the deed - an ancient female red and her younger but still rather old (and thus technically "ancient") blue consort. I'm imagining that while the blue took out the mithril golem guardians, the red figured out the flaw in the city's defenses (perhaps through treachery) and was able to collapse a cavern filled with most of the city's population. Or something like that.

Any thoughts, ideas, misgivings or fears?

Thoughts:

• The standard tactic when trying to tackle an ancient dragon with low-level warriors is to rely on mass archery and the law of large numbers. This does not work in an underground city, where combat takes place in confined spaces and only a relatively small number of dwarves can engage the dragon at any one time. The city's regular defenders would be very hard pressed. It's quite plausible IMO that one dragon could do it.
• Furthermore, siege defenses that rely on heat and fire (boiling oil, molten lead, etc.) do not work on a red dragon. They do work on a blue dragon, however, so if there was a head-on assault involved, it would make sense to have the red dragon take the lead.
• If the city had a force of golem guardians, that'd be a different story. Golems are very, very tough customers, and several of them could go head to head with a dragon--especially since the dragon couldn't engage them from the air. I assume you have the blue dragon fighting the golems because mithril golems are similar to iron golems and thus immune to fire? Iron golems are immune to non-magical weapons, so the dragon could only hurt them with elemental damage.
• The obvious siege defense for an underground city is to drop rocks on the head of the attacker. That works even on a dragon. I would expect the main gates of the city to have a last-ditch mechanism that could be used to collapse the whole tunnel. The dragons would need to disable that if they wanted to break in through the main entrance.
• The weak point of any big city is its supply of food and water, and that goes double for an underground city which can't grow its own food. (Mushrooms don't need light but they do need nutrients, and those nutrients have to come from somewhere.) One of the dragons could find and cut off the dwarves' source of water and/or food, while the other prowled outside the city slaughtering any who left the shelter of the city's defenses. This also gives you the opportunity to put in some nice, chilling, Moria-style memoirs for when your PCs explore the ruins: We cannot get out. We cannot get out.
• Pursuant to cutting off the water supply... don't black dragons have a regional ability that lets them poison water within some large (a mile or more) radius of their lairs? The dwarves, not being stupid, would have their supply routes well protected, but there wouldn't be much they could do against that.

 

[KarinsDad]

But yeah, I agree that ancient dragons should be, if not the most powerful monster in a D&D world, up there with the others. As it stands I'm guessing that a tarrasque would defeat an ancient red...hmm, that's almost thread-worthy.

Not very thread worthy. In a straight up fight, the ancient red would quickly realize that its breath weapon does nothing, dropping boulders on the tarrasque does nothing, and melee combat is advantage tarrasque. But the ancient red has one advantage that the tarrasque does not. Int 18 vs. Int 3 and the tarrasque has no ranged attacks. The dragon intimidates a few other young or adult other color dragons into flying over with breath weapons until one of those weapons actually work (e.g. a young white dragon could defeat a tarrasque by never getting into range and just using breath weapon).

 

[Trickster Spirit]

Good stuff, thanks. Yeah, I think I can stick with my initial back-story - I just wanted to make sure it wasn't too far-fetched. I might even have it that the red did the deed herself, the the blue came later and courted her (the reason I want both is that eventually I hope to have the PCs take the city back, but they'll fight and theoretically defeat the blue, thinking that it is the dragon, and then find that it was merely the consort for a larger, older, more powerful red).

But yeah, I agree that ancient dragons should be, if not the most powerful monster in a D&D world, up there with the others. As it stands I'm guessing that a tarrasque would defeat an ancient red...hmm, that's almost thread-worthy.

Keep in mind that using the dragons-as-spellcasters variant would make it even easier for the dragon to overpower any resistance / evade overwhelming numbers of dwarves. I don't have my books in front of me, but Enlarge/Reduce, Invisibility/Greater Invisibility, Gaseous Form, Stone Shape, and Polymorph all sound like spells that would help them get around and launch surprise assaults on the woefully unprepared and terrified dwarves.

 

[bleezy]

It would take as few ancient dragons as you would like. The lair actions and regional effects are supposed to suggest that the dragon can do whatever it wants; it could make a volcano erupt and kill 10K dwarves if it wanted to. It could poison the water with sulfur, cause an earthquake, etc.

 

[KarinsDad]

It would take as few ancient dragons as you would like. The lair actions and regional effects are supposed to suggest that the dragon can do whatever it wants; it could make a volcano erupt and kill 10K dwarves if it wanted to. It could poison the water with sulfur, cause an earthquake, etc.

It takes a while for a lair to be created. It sounds like the OP is talking about the situation of before the dragon can change the dwarven home into its lair.

 

[Quartz]

Two words: spawn and minions. Your dragons have an army of minons (e.g. kobolds, with an efreeti commander or two) and a good number of spawn. One of the nice things about 5E is that the biggest monsters aren't invulnerable to mooks.