Derren said:
It depends on the age of the dragon but generally cities are strong enough to repel or pose a serious thread to most dragons., With the "20 always hits" rule, 500 level1 archers each firing a +1 arrow /greater magic weapon) will score enough hits on any dragon to kill it. And that doesn't even take the level 14+ characters into account which live in a typical D&D city.
OMG this topic is still going? And it has spread to a new thread to boot. Well, I have nothing better to do at the moment.
First of all that is a LOT of assumption that you will get that many archers ready to shoot WITH magic arrows without a good bit of advance warning. Only an idiot of a dragon would ever give the city that kind of chance to get ready.
Here is what will actually happen
1. Dragon gets pissed off at the city for some reason. Maybe they didn't pay their tribute on time or something.
2. Dragon takes off and flies to attack the city at night when the mortals can't see well (and giving it a miss chance). Not wanting to give the pathetic mortals time to flee or any chance to spot it, it comes in low and away from the main transport links (rivers, roads etc.). Without potent magic at their disposal (some sort of divinatory magic alerting them that the dragon will attack today) and with darkness and typical guard alertness, (playing cards, drinking, daydreaming or just looking the wrong way because guard duty is boring) the dragon isn't spotted until extremely close into the city.
3. Fear and indecision sets in among the spotting guards. OMG the dragon is out. Where is it going? Is it going to attack? (Minutes pass to confirm that it IS approaching to attack, as the guards do not want to sound a false alarm).
4. The guards sound the alarm (speaking tubes or bells or something). Assuming a special signal for "the dragon is attacking, this is no joke," and if the troops are very well drilled and have had some recent practice to keep them sharp, a decent portion of its defenders start rousing themselves from whatever they were doing, suit up, get their weapons and leave their homes/barracks and attempt to marshall at a location. Hopefully enough archers are actually in the city and not deployed to guard positions outside.
Unfortunately for the nearest wall guards, they don't live to see it as flames engulf them. Being 4th or so level maybe, they can't hope to survive even if they save. The dragon takes care to set fire to everything flamable for maximum terror and destruction and maximum concealment from smoke. The city then does what non-modern cities historically did when confronted with fire . . . they burn . . . a lot . . and very quickly.
5. The population realizes that the attack is real and the dragon is upon them and they do what they do best - PANIC!. People flee everywhere they think is safe. The weight of panicking crowds severly hampers the defense. Fear being contageous, some of the defenders even rout and flee themselves. Others are knocked down or pushed aside or succomb to smoke or fire or collapsing buildings.
6. Meanwhile the dragon roars in delight and burns everything and everyone it can. Smoke and fire are everywhere. Smoke stings the eyes, and clogs the lungs. The dragon burns any group that looks like it is forming to attack. Then when it is satisfied it flies off while the city burns.
In conclusion, your supposition about the 500 archers isn't going to happen. The city's best chance actually is that a group of adventurers or other high level individuals who are practiced in this sort of thing survived the surprise attack and went into action quickly. The city army's strength is in numbers and no dragon will give enough warning to build up the numbers to defeat it. Even then they wouldn't face good odds unless more powerful than the dragon because they'd have no prep time. Casters would be down spells, armor-users wouldn't have gear on (or necessarily even nearby) etc. They'd be better off waiting and pursuing the dragon to its lair.
Watch
Reign of Fire or
Dragonslayer or simply
Tora, Tora, Tora (for a typical response to a surprise attack) sometime and you will see how hard it is to fight a dragon that you didn't see coming or to rally any defense in the face of a surprise attack. Speed, surprise and general terror are powerful weapons and a dragon doesn't need magic to employ them.
And the dragon in this example has NO minions to fight or simply spready discord or sabotage the defense.
Tzarevitch