Telantha is the last known surviving city after a cataclysmic event that occurred approximately three years ago resulting in the gradual (over four weeks) destruction of most of the world and the appearance of a substance known as the darkness.
To the best that people can tell, the darkness exists above the uppermost cloud layers. As the darkness appears to be non-reflective, it's impossible to tell whether it actually has substance, it only known that no light can penetrate it or reflect off of it. Spells and projectiles have been thrown up into the darkness with no effect - these experiments suggest that they simply disappear into the darkness, leaving no trace.
Beneath the darkness is where lies the true danger to the mortals of Aagos. Although the people and eventually the land would of died without the light from the twin suns of Cymur or Balor, most incurred a much more rapid death at the hands of the demon-like creatures that ravaged the land. Distorted creatures both similar and yet so radically different from the natural flora and fauna that populated the continents. Demons that ranged from something no bigger than a rabbit, and others immense enough to be compared in height to a dragon. And yet all are deadly. And so the people of Aagos died in the hundreds of thousands. With their throats ripped open, with their entrails dripping into the blood stained earth, with their limbs torn from their bodies, leaving a world of chaos and death.
All save for one solitary place. One city not too far from the East coast in the Kingdom of Viroth. Telantha. In this conservative town the people - whether it was through the priests praying, the mages spell casting, the guards strong arm or the intervention of Cymur himself - were able to push back the darkness covering the world and claim the sky back once more.
Although the demons occasionally ventured out of the darkness and into the light, it was no longer quite the onslaught of creatures within it. Those gathered within Telantha - Nobles, citizens and refugees from all over Aagos worked together - or fought together as the case may be - to keep the last remaining pocket of civilisation alive.