The History of Takarez' Lost Kingdom; Aqui

"Thousands upon thousands of years ago, one of the greatest calamaities ever recorded occured, sending an entire civilization, advanced for their time, spiraling down to ruin. Now today? Echos told by maddened undead, and broken memories of a race that clammers in fragmeneted remeberence, to wage war against the gods who forsakened them."

— Aqui Historians

The Lost Kingdom of Aqui was once named the Shining Pearl of Takarez; Aqui. They were purveyors of all things scientific, and were first masters of alchemy before all else. They owned most of the centralize northern strip, even far before the elves, and before Isuth split into the two continents known as Takarez and Isuth during the human civil wars. It was considered a free city, yet at the same time, still possessed several towns alongside their main one along a river that cut from the land bridge of Vassalstar all the way through central Takarez. This city settled on the river was a flourishing spot for trade. They were very closed off from the rest of the world getting a peak inside however.
The average lifespan for an individual of their race, which was referred to as the Yuan-ti was only a simple 150 years. Very close to humans, even despite being unable to cross breed, those who looked too much like their Takarez neighbors were completely outcasted from their society. Their barbaric nature of the higher classes of Yuan-ti established a rigid caste system that sought to keep the noble blood pure, as the more brown and yellow traits were dominant and the rarer greens, and especially black and white colorations.
While the black and white colors were meant to symbolize their unique dedication to worshipping both the Dhedes and Sairin pantheons, eventually as times went on this became more tradition than something that was actively drawn to by the Sairin and the Dhedes beliefs. After a short one thousand and two hundred years into their kingdoms founding, Aqui fell out of its worshipping practices and became the first of its kind, a kingdom that did not place belief in the gods to guide them.
This was all to be considered, extremely new. The gods got really too into inhabiting individuals within the kingdom to experience a place that did not worship him. On record it is said everyone from Rendrus to Idayiom himself inhabited a Yuan-ti to experience it. But the one who actually inspired them the most was the god Sabreal. Sabreal was worshipped largely by the kingdom when they still worshipped gods, and them falling out of his graces hurt his power source substancially.
The hieroglyphics on ruined walls tells the tale of a minor disaster best tranlsated as 'The 13 Hour Hunger'. It is unclear what exactly happened, but the depictions show many Yuan-ti falling into a black spiral.
Regardless of this event the civilization pressed on from their punishments. Patronic celestines were executed shortly after they were discovered, a fact that greatly pissed off the gods inhabiting them.
After being forbidden from magic upon executing one of Idayiom's celestines, the racial kingdom rebelled, setting their sights on taking the power out of the gods hands. They were remarkably efficient for their time, creating the basic makeup that would later go on to permit laz-khad infused technology to exist. These things would power everything as arcane conduit stones. From ships to lights to labrotories.
After ripping the power of magic from Idayiom's hands, a thing that while annoying, Idayiom is remarkably dismissive of the habits of mortals. No, but they crossed a line when they decided to take their short lifespans in comparison to their elven neighbors into their hands, and focused on necromancy.
The race when they rebelled against magic also by effort rebelled against resurrection magics, and this for a few hundred years plagued them. Until a breakthrough. No one knows for certain who came up with it first, but some one, some how, lost in the transcripts written in hieroglyphics on the walls, found the secret to undeath.
And not the undeath that Sabreal puppeted, but a new one, or Sabreals but altered. Experimented, and switched around to allow them to keep their sentience, their free will, and even unlock magic once again despite the gods forsakenment of it.
The Kingdom of Aqui knew how to break the rules, and unfortunately, this forbidden knowledge would lead to their downfall. It isn't clear exactly what happened, but what is known is a war was waged, as Sabreal split the mountains in Takarez opened and called all Necromancy dragons forth, from the tinest Wyrmling to Hades himself. He puppeted an army to charge and destroy the kingdom. It worked for a while, but when they began to repel the dragons, it is said Sabreal tore the world asunder from below, and caused the calamity known as the fall.
If the fall itself did not kill you, Sabreal summooning a Celestine form of a Great Wyrm would, as he breathed in the souls of those who remained to kill them. Some were able to tether themselves with the arcane souls serving as shields, but the damage was unrepairable.
If the calamity didn't kill them, the foodless, waterless underground landscape did within a few weeks. Those who could find the resources or had them on hand turned themselves into mummies, a whole lot of them turning themselves into feral mummies unknowingly from unexperience or simply not knowing how to do the ritual properly.
There was no saving the kingdom, as now all that remains is a sunken city, caught between the surface and the Underbelly of the world.
The phraoh of Aqui at the time is unclear, but all know by Sabreals very public decree, that all of the royal family shall be cast into the deepest parts of the underbelly's crust, to suffer and languish until he deems their torture enough, and not a moment sooner.

The Color Caste
Untouchables were those with brown scales, said to resemble the humans of Takarez far too much, and as such were cast out socially, to not even be seen as people worthy of respect. Sudra were those with yellow scales, they were the commoners, peasents, servants. They generally were not allowed to hold any sort of political position and were often denied services that would be reserved for higher castes. Vaishya are lime green in coloration of their scales, they would mostly be a caste made up of merchants, and land owners. Dark green scales were those of Warriors, Generals, and individuals trusted with higher govermental positions. Kshtryia were those with Black Scales, said to be royal by birth and nature alone, often growing sleeker than their kin and having what was considered in their society, beautiful and preservable features. The only ones that outranked the Kshatryia were those born of pure white scales called Bhramin. They would be considered the closest to being divine, and if a Bhramin was born within the royal family, the king or queen at the time would be expected to step down before the child turned ten (which, bare in mind, was still very much in their youth.)