'Be prepared for a lecture' or 'I'm too lazy to write a new shorter description and recycle old stuff'.
My Homebrew: Taken From My Story Hour (Link is in my sig).
The setting is a city named Serpent City. It is placed in the western continent of the world, which was first settled about 700 years ago by humans from the then-all-powerful Kentaarian Empire (that's sometime in the 11th century of the Kentaarian calendar). Before that the only sentinent races in the continent were gnomes and orcs. At first, both the gnomes and the orcs neither liked these new strange invaders and tried everything to stop them. The gnomes quickly changed suits after the Kentaarian army crushed and enslaved the whole orc civilization in one strike. Instead, they greeted the strangers with open arms, glad to be rid of those pesky orcs who had been tormenting them for milleniums.
Serpent City was the first city to be founded by humans in the new world. It was built from stone taken from the mountain ranges west of the city called Shadow Mountains. The spooky name comes the fact that the rocks the mountains mainly consist off are completely black. Therefor, Serpent City is nearly all completey black too.
About 400 years ago some gnome miners discovered a mysterious new blue-ish alloy in the southern mountains of the continent. The gnomes named it Thunderstone because of it's explosive qualities. The gnomes, who are known tinkers, were able to create such things as gunpowder and explosion combustion engines from this magical substance. Big markets formed around thunderstone products. When this thunderstone tech was combined with the age old human magic disciplines named Rune-Smithing (kinda lowpower magic item creation) by the tinkers of the gnome city Harrgard, such things as wargolems (big metallic warmachines, not always humanoid in form) and aircruisers (flying ships) were created which completely revelutionized the world's way of warfare, travel and trade.
When the aircruisers became the main tool of travel and trade in the world, the spires were built in many of the main trade cities. Colossal towers often up to 250-350 metres in height. They function as both multilevel docking stations and warehouses and as gigantic market places. The biggest one of them all is the the Serpent which is located in the centre of Serpent City (the city gets it current name from the construct). Like the rest of the city the Serpent is made from completely black stone, except for the huge silver dragon statue that sits upon the top of the spire and circles it's tail around the spire all the way down (a long tail, that). The idea is that the dragon sits upon it's treasure (the treasure being the spire and all the riches it holds).
But the denizes of the western lands were not so happy, because all the profits from the thunderstone went straight to the Kentaarian Emperor. One day Lord Julius Dracani and his followers of New Leiteinscheir, a city south of Serpent City and east of Thunderstone Mountains revolted against the Empire. In the course of the following year all of the Kentaarian colonies except for Gromnburg (a city north of Shadow Mountain) joined Lord Dracani in the war. The war lasted for nearly a decade, or until the old Emperor died and his son took over, who thought that the war wasn't going be won and it would be better just to let them go. And so the western world got freedom to do whatever it wanted.
Some of the southern colonies joined New Leitenscheir into the Dracani Dynasty, ruled by King Julius Dracani I and some of the northern ones (like Serpent City) followed King Kerak, but most remained independant. But Kerak quickly came corrupted by the power and craved for more, so he raised an army and marched south. Kerak's war efforts did though not go well and lost all his followers outside of Serpent City. Then he confiscated the Serpent City's Merchant Guild's aircruiser fleet to aid him in his war efforts. This decision backfired on him though because without the fleet, the guild went out of business, this didn't exactly sit well with the guildmasters so they revolted against Kerak and chopped his head off on the palace's balconies. Now the Merchant Guild controlled Serpent City and they later founded the Union of Free Cities (usually just called 'the free cities' or 'the union') with some of the neighbourhood cities (all of which are now controlled by the guild).
The players play cops in Serpent City.
