Pt 1. A Violent Birth.
Long, long ago, a formidable volcano coughed its final atmospheric cloud and expired. This geological titan's passing left a rich, fertile, finger poking out into a smallish sea known as MerKressus, its jagged peak can be seen from virtually every surrounding shore. Thousands of years of seaside erosion had carved the conical giant into more of a sloped semi-circle leaving it accessible from one side, but its knife-blade edge still protrudes impressively from its peninsula and serves as a reference for navigating MerKressus.
The first settlers in the volcanic corpse unknowingly set in motion a series of desperate battles for control of this natural fortress and it's a wonder that the imminent rocky shore is not permanently stained by centuries of bloodshed. The volcano took on the name Sikorset which translates to "deepest bite" , which is interesting because it likely had a different ominous name in its more aggressive days, but, here I am just speculating.
The earthen fortress was a prize for its resources and location but as with any prize, it was so sought after that actually enjoying its advantages was rare and carried the constant burden of risk. Planting and growing food in the soil around its outer crust resulted in local tribes plundering and burning the yield. Attempting to trade with other shoreline settlers was met with jealous hatred and typically turned ugly. It was, in essence, the curse that everyone thought they wanted.
This continued siege after siege, one culture building on the bones of another, until nature itself began its own assault.
The most successful civilization to put down roots in Sikorset's belly was led by a shrewd king named Gemoretzach. His carefully plotted strategy went beyond the initial siege and seizure of the fortress because he knew that the only chance they had of holding their position was to quickly refortify and lay down infrastructure before anyone could pounce upon their wearied army and piggyback on the victory. I will spare you the details for now but, suffice it to say, he achieved his goal and established a fortified city to then modern specifications in a breathtakingly short amount of time.
It was not long before nature's aggression became apparent. The interior of Sikorset is naturally moist, like a warm cave. Countless species of moss, fungus, mold, and carnivorous slimes had developed intricate colonies all over the interior of the crust and the bodily excretions of former inhabitants and their actual corpses had only served to expedite the growth process of these ever expanding non-sentient residents. For a humanoid species that had not evolved to endure the impact of spores and diseases associated with slime and damp conditions, this had become a toxic atmosphere and they hardly had time to react before it began to take its dismal toll. The civilization collapsed at an alarming rate, succumbing to a biological assault it could never have prepared for and word spread that the gods had grown weary of this monument of greed and had bestowed upon it a deadly curse.
The volcano, once again, sat dormant. That is... until the Slimelord discovered it, filled it with fishoids, and named it Seschakrutz "the moss fortress" or, a more human friendly word, "Mosschester".