Once there was a magnificently opulent city.  Its citizens were used to the finest things in life.  They lived with fantastic wealth and luxury.  Thus they had many who were envious of them and desired to take that wealth from them.  But money buys quite a lot of protection.
  This city was fortified by the finest of guards, strong and tall white walls, and some powerful wards against massive magical attacks.  Truly, the citizens had bought protection against all the most major forms of attack.  Try as their enemies might, they could not penetrate this city to loot its fabulous wealth, no matter how much force they applied to the problem.
  And so the rich city lived at relative peace for some time.  Until a particularly crafty rogue came to the area.  Not just any rogue, this one had also had training in some dark magics.  He came to see this 'impregnable' city full of wealth.  A challenge, as he saw it.
  As luck would have it, he came to town as another warlord was assailing the city.  The Warlord had mages flinging massively powerful spells, archers firing barrage upon barrage of arrows, and his infantry trying to access the gate, guarded by the ornately decorated yet fearsome troops.
  All these things failed.  Miserably.  The magics were reflected back by the magical wall around the city, the arrows could not reach over the towering alabaster walls, and the infantry were no match for the gate's guards.  The warlord could do nothing but retreat in defeat and shame.
  The rogue simply strolled up to the gate afterwards, to see what would happen.  The guards eyed him closely, seething with a magical aura, but let him pass.  He was no threat, after all, just one unarmed man.
   Inside the city, the rogue was assaulted by the heavy scent of perfume.  Exotic flowers grew almost in every window, and indeed, scented oils and perfumes seemed to quite fashionable in this place.  Shops selling the scents of the city were literally upon every corner.
  All well enough, as such things are quite valuable.  The rogue was considering his options when he happened across a fellow he recognized... Another rogue, no doubt planning his own theft.  He watched with a smile as he saw this fellow slip a few vials of the scented oil in a nearly undetectable manner into his cloak.
  As his fellow thief headed nonchalantly toward the gate with his booty, the rogue was educated further as to how this city kept its wealth intact.  The guards at the gate reacted faster than the wind, swinging a heavy sword at neck level.  The poor thief had no chance to react; he was decapitated instantly.  The guards had somehow known he had stolen goods upon his person.
  The rouge smiled.  This was indeed a challenge.  He spent the better part of the day scouting the city, making notes of all the most valuable caches of wealth.  After a time, he had formed a plan to exploit the one and only weakness he had seen in his tour of this marvel of a city.  He left the city to prepare.  The guards grunted as he left.
  He returned the next day to the city gate, with a small cage.  He once more entered the city without incident.  Trade is, after all, the lifeblood of a city,  and a cage is not a weapon nor a threat.  Once inside, the rogue headed into an alley and cast a very minor spell upon his caged plan and set it loose within the city.  The rat ran squeaking into the shadows.  Smiling to himself, the rogue left the city, and simply waited.
  Within a moon, the opulent city was quiet as a tomb.  The rogue returned to loot the now empty city.  Empty, that is, aside from the usual contingent of vultures and looters that catch wind of such devastation.  He knew precisely where to go to find the most valuable of things, some of which he had 'rearranged' during his tour of the city.  The other looters present were primarily taking the myriad of scented oils, which had been this city's undoing.
  For this city had a fondness for scented oils, and did not see much point in washing the sweet smell from their bodies.  A minor contagion placed upon a humble rodent had wrought great devastation upon an overconfident populace.  Their lack of hygiene not only preserved the sweet scent, but the contagion as well.  The citizens laid lifeless in the streets, no longer moving, nor smelling quite so sweet.  There were even signs afterwards of panicked merchants trying to flee with their goods, but, even weakened by contagion, the magical gate guards had slain them as looters before collapsing themselves.
  The overconfidence and pride of this rich citizenry had not allowed them to see a lesson they could have used...

 It takes but a small wound to kill.