Falon-nir began as a settlement created by Falon the Conqueror after his conquests, one of several where he settled those of his warriors that decided to remain with him in lands they conquered. It was the biggest one of them all, and grew even bigger after Roma - imperial capital during Old Empire Period - collapsed into magical anomaly during the Dawn War. It was named a new capital of the Imperium... and grew. Today - despite being ruined multiple times and rebuilt - it remains the greatest city of the Imperium of Karadia as a whole. With nearly three million inhabitants, and the centuries of hoarding wealth, it is exactly as glorious and great as a city can become, overtime growing heavily into a supernatural world and even having direct connection to Imperial Religion as a whole.
Most cosmopolitan city in the Imperium. It is divided into many districts, many of them being pretty much a small version of other lands imported right into the very middle of the Imperium as a whole. Each of them with many individual festivals that make the city a rather... colourful one. Most of the inhabitants are in one or another way connected to the vast machinery of the Imperium, even if indirectly - for example by making sure that its beaurocrats and so on have a place to buy food in.
Each district is pretty much self governed. There is also a City Council that oversees their work as general.
Defended by a separate (and considered elite) army of Imperial Army, forces of various imperial organizations that have their headquarters there, not to mention many powerful servile daemons of White Pantheon (and even some of Black Pantheon) that live in local shrines and temples (considered more holy and important than those on the outside), that due to the nearly sacred nature of the city react to outside threats (especially supernatural one) by materializing and slicing people around them to death. Generally speaking the city was never fallen to outside enemy. It was only threatened during major civil wars in the Imperium, always being important enough for its holder to be considered the most important one. Also almost always it was a separate 'city-state' for a while, held by remnants of a pre-civil war imperial government, remaining neutral but being ready to crown the winner in the war outside of it. If it actually was a side in the war, it either gave its holder enough power to win, or simply surrendered after its holder armies were decimated outside of it.
Major center of a trade and industry. It holds some of the most important metalworks, best alchemical plants and major technomagical factories. All of them are characterized by an extremely modern approach to things, including insurances for workers that also have guaranteed small number of stock of their factory and so on and work slavery is practically nonexistent. This is the beating heart of imperial economy, that creates intense ammounts of highly valuable goods.
While the city itself lies few dozen kilometres from the coast, it is connected to the expansive harbours via permanent Aether Gate, overtime practically consuming the harbour town, making it officially a part of Falon-nir. All districts have expansive sewer systems, are divided by walls and have their own granaries and medicine stores in case of either prolonged siege or epidemy (in both cases made last much longer via entropy magic). Their gates are fully automatic and made from steel reinforced with antegnite, being practically unbreakable, allowing an easy separation in case of daemonic incursion or epidemy. Many more prosperous districts (there are no slums in the Falon-nir, so they are on average quite decent as a whole) even have a surviving automata from the time of Great Karadian War that keep the peace on the streets with deadly efficiency.