The Sciro and the Annelids
The depths of the world are home to a history deeper, darker, and stranger than the people of the surface know, and calamitous shifts in the world happen without any word reaching the world above. There are few things that exemplify this more than the fragmented former empires of two ancient races, the Sciro and the Annelids, whose terrible wars shaped the mythology of the world below.
Before we go into details of their histories, however, we must know who these two races actually are. The Sciro are an arachnoid people, clad in black carapace and with four legs and four arms, the top pair of which end in durable, powerful pincers that are typically used to crush stones into smaller, more easily-manipulable pieces. The Annelids, meanwhile, have upper bodies similar to hairless gorillas and lower bodies best compared to serpents, though legend goes that they were once most similar to worms; they find it easy to tunnel through earth, but areas of solid rock are obstacles that must be gone around. Based on these physiological differences, it is believed that the Sciro evolved further down than the Annelids, as stone becomes more common the further down one goes; however, both races frequented the caverns more often than they created their own, and it would be here that they would come into conflict.
Perhaps these races could have interacted with each other peaceably, still, had it not been for their religious differences, as each race's favored god bore similarities to the others' most hated figure. The Sciro worshipped The Nameless, a god of magic and craftsmanship whose myths most frequently depicted them overcoming Taurc, a brutish god of lifeless stone and selfishness, rumored to have stolen the Sciro from their old home in the sky to place them deep within the underground (modern scholars agree that there are no signs of Sciro evolving anywhere but the underground, due to noted genetic similarities with other organisms in the ecosystem). The Annelids, meanwhile, worshipped Toron, god of gravity and earth, who overcame the torments of a Faceless trickster-god with the endurance of stone, unrelentingly powering through their schemes until the trickster was forced to relent in order to save their own skin. Naturally, each race seeing the other worship a being they despise could only lead to conflict.
Interestingly, both mythologies revere an entity known as the Lifebringer, though in different ways; the Sciro worship them as the creator of the plants that fill the caverns, while the Annelids thanked them for the air they breathed; both believe that the Lifebringer created the animal life of the underground, from the smallest prey to the greatest predatory monsters, leaving them a figure to be equally respected and feared.
These thoroughly different religions, and the philosophies that come from them, lead us to the ancient empires of these venerable races. Sciro society, in its earliest days, was led by tribal wisemen, and as their civilization developed, it was those who could most prove their wisdom who were most respected, with their government developing into a strange form of semi-democratic meritocracy where highly-formalized structures of debate were used to identify those with the capacity to lead, and their culture giving most respect to innovators in the arcane arts, craftsmanship, and other such fields. Druidry came to be a prominent art in Sciro society, with practitioners being able to mold the stygian flora into useful forms or direct new growths at their whim.
Annelid society, meanwhile, turned in a martial direction early on, though with a much greater focus on the ability to defend the tribe than on the ability to project power; early chieftains were frequently chosen through trials of endurance, such as remaining atop a bed of hot coals for as long as one can; although these rituals fell away with time, Annelid leaders continued to have a system of dual leadership, with a military leader recognized by the full society and lightly holding authority above a more-distributed civilian government. So, too, did their culture more heavily emphasize professions requiring enduring physical exertion - the military, yes, but also miners, blacksmiths, and the like; other occupations, while not disrespected, were seen more as supporting the work of more-physical ones. Their culture did not, however, trust those who relied upon magic rather than material solutions; in their conflict with the Sciro, this drove them to the development of ever greater feats of metallurgy and crafting, with artefacts recovered from shortly before their empire's collapse nearing the quality of modern dwarven steel, which requires the use of runecraft in its production.
The wars between the empires that the Sciro and Annelids carved out have still left their marks on the caverns of today; grottos overgrown with the wild and dangerous products of feral druidry are often the source of beasts that must be killed to protect towns and cities, while every miner knows to be careful where they prospect, lest they unwittingly set off an ancient Annelid explosive or other trap. So what happened to these empires? The story is better known with the Annelids; a great dragon came to rest near their territories, and offered their people great treasures should they bend to its will. This set off a great civil war within the empire between those who wished to take the dragon's gifts for their own and those who were enraged at the thought of relinquishing their freedom; although the Adherents of the Wyrm were victorious, it was the loyalists who had the last laugh, as a group of insurgents, once members of the old empire, managed to sneak into the dragon's lair with a large quantity of blast powder and assassinated them, though none survived the mission.
Sciro society had a stranger disintegration; with their eternal enemy in chaos and no longer able to war against them, the Sciro no longer had much of a common enemy, and disagreement broke out over what was truly the best way forward. With the event being so long ago, what we have left of records are all legends, and many contradict each other; some claim that the Sciro, like their old enemies, fell into civil war, others claim that independent states were carved out of the old empire through mutual agreement, yet others say that these states came about just due to different sections of the population eventually deciding to stop listening to their political opponents, and more claim that the empire whittled itself down by exiling dissidents until it was no more powerful than the splinter states it had inadvertently spread across the underground. Whatever the case may be, just as the Annelid empire collapsed, so too did that of the Sciro.
So where has that left the two races today? Neither went extinct, after all, though the change in the Annelids' form is clear.
There are numerous Sciro city-states throughout the underground, but the Sciro themselves are more likely to be found having integrated themselves into more cosmopolitan civilizations, especially those with strong traditions of scholasticism or craftsmanship. Only a single Annelid state came out of their collapse, but it remains an influential one to this day, with the Adherents of the Wyrm still having a notable voice in the international politcs of the underground, albeit a much-reduced one in the face of various rising powers such as the dwarven Urick Confederacy and the drow Eight Families; beyond their borders, there are numerous respected Annelid mercenary companies and mining corporations. Though faith in the old gods has faded among both races, it still competes with more modern religions, both of the rising powers and those imported from the surface; the tensions these faiths caused, however, have mostly disappeared, with discrimination against the other race now being looked down upon rather than assumed as fact. Cultural works from Sciro and Annelid history remain, considered classics by modern underground society, and they are commonly subjects of study to see how they have affected the stories and art of the world below, both in the past and the modern day.