The ruined city once had a name, and a greater place that it holds now. It was part of a bustling trade route, a stopping point for caravans and wagon trains, bundled down with goods to trade and gold to spend. The people were industrious and content with their lot, such as were the majortiy of people who live in a city of moderate size. This was not to last. Fate played its hand, and ruination was delivered to the city. It suffered three strokes of bad luck that brought it to its knees and thence to its grave.
Raiding is a day to day matter when the neighbors are orcs and goblins. A new leader rose among the scattered clans and the raiding became more focused, and inflicted increasing damage, slowing trade and raising the cost of defense as more and more mercenaries were bought to defend the roads and bridges.
The mercenaries brought something with them that was more hazardous than the orcs who raided from the wild. With their baggage trains of supplies and food came rats from their distant country, carrying fleas, and strange diseases. The orcs and the humans alike were savage by an outbreak of the illness. Fevers, dysentary, tremors and death ran through the populace like wildfire. The city was made desolate, and rank with the smell of death.
Cities have recovered from the breath of the necrotic gods of plague, as they have endured raids and civil war. The ruined city was dealt its final card. A civil war, short lived and violent began, and the city lost any importance it had as the fighting reduced its province to a wilderness. The surviving populace moved away, seeking better luck elsewhere, in other cities, or with their families.
The city did not remain fallow long. It was soon reinhabited by the worst sort. Thieves and outlaws, murderers and brigands and assassins found shelter in the ruins. Most the houses still had rooves, and offered good protection from the wind and the rain. Why live like a petty beggar in a living city, when a mansion could be had, or the hall of a local prince who fled when the illness came, and never returned when it had gone. It is a Hobbsian place, where strength is the only rule, and success the only law, and death the only consequence.
The city has not been deserted for ages, but on a scale of decades, but less than a century. There has been no maintenence of the infrastructure, and the buildings that survived the raids and the plague are failing to attrition. Rooves sag as wooden members slowly rot, holes go unpatched, and spread. In many places, the plaster is flaking off of the buildings, and the wood has turned a sicjly chade of gray. Lighter structures have fared the worst, collapsing during storms and going unrepaired, while the stonework has faired much better. The feel of the city should be one of decay, and wreckage.
The Thief King - The city of thieves, long forgotten as a place of decay and suffering has discovered a new vitality. A new boss has made himself a Robber-King claiming the city as his domain and its inhabitants as his fief. He has gained some support, and now the thieves and murderers are more organized and starting to make their presence felt outside of the City. The PCs are drawn into the plan to seek out the source of this new leader, or conversely are drawn into his cult of personality as vassal-thieves and mercenaries themselves.
That Which was Lost - Many wealthy and powerful families deserted the city during the darkest hours, and never returned. It was a dead place, and filled with the blackest of hearts. Not everything could be taken and some things were hidden away for a return that never occured. The PCs are sent into the city to recover the McGuffin and return it to its rightful owners. Complications - aside from the thieves are riff-raff who now populate the city, the item might be part of a bandit-lord’s treasure pile, might be hidden inside an assassins lair, or might be a trophy of the afore mentioned Thief-King
No Escape - In persuit of a thief who has stolen the Dingus from Lord X, the PCs track him to the outskirts of the ruined city. Do they play up the legends of the place being a haunted place of ghosts and demons, or charge in to valiantly do battle.