There are many legends that tell of the founding of the Salassian Empire. This the most common one, but it is not necessarily the most true.
Over a millennium ago, Sala emerged from the Underdark, after have brokered a deal with Lolth for at least some of the Sun back. Sala set what was left of Pelor free, and went about the business of building up what was first a kingdom.
The First Great Law
Sala’s first edict was that all writing and arcane knowledge was her domain. Only herself and her devoted clergy were permitted literacy, and any written works were systematically collected or destroyed.
As a result of this edict, wizardry and arcane magic became extremely scarce within a generation.
Wars of Conquest
This was not enough for the Empress. The First Great Law needed to be enacted in every land, and the empire went about making that happen. Kingdom after kingdom was routinely subjugated. The Empire had resources that others did not.
The empire quickly mastered key resources that others did not have. Everflame and Bloodsalt would win more battles for the Empire than any undead legion.
However, the true advantage the empire had was time. The core power of empire was held in undead hands that could wait and plan for mortal generations.
The Endless Stair
Sala herself poured a vast amount of the imperial resources into building what is now known as the Endless Stair. Rising out of the imperial capital of Throneseat, the Stair is a tower that now reaches into the heavens.
At the inception of the Stair, countless workers and resources were used. Requests would come constantly from the rising apex of the tower for more materiel and slaves. Centuries later, those requests can have years between them. The requests are increasingly odd and usually nothing to do with construction.
The Twenty Rise
As Sala was consumed with the building the Endless Stair, the implementation of the Empire was delegated out to trusted subordinates. These were a mix of undead, mostly liches, some vampires, and some that defy anything but their unique name as a description of their unlife.
These functionaries were first jokingly called the “fingers and toes”, as a joke referring to Hand of Vecna. However, this has become more codified, and they are the Twenty.
Much about the Twenty is shrouded in mystery, since they are almost never seen except by their inner circle of mortal subordinates. It is commonly known that there are never more than twenty of them, and they are bound with powerful magics to Sala. It is also known that something keeps other undead from rising to their power, if only fratricide.
The Eyes are the inquisitors of the Empire, tasked with routing out corruption and threats to the Empire. They are almost entirely mortal, and the subjects of their inquiries are also exclusively mortal. Everybody fears this police force, which works largely in secret and with little oversight.
Once the personal domain of Varjo, the Hand is the military of the Empire. It is a mixed undead and mortal army, with tactics unique to that structure that make them a brutal and effective military.