This event was referred to by the Apostates as the Terchian Heresy, but to the Terchians it is a great event in their history.
Long ago, large numbers of humans were kept in the ancient city of Arathaea in the deep south of the Arathaem Desert. A boy named Saint Tarsius under the oppression of the people encounters a divine occurrence whilst gathering wood in the outskirts of the city of after coming in contact with an unknown force. This force is the One God who appeared in the form of a mighty being of pure light and energy. The founder would then make claims of divine communication and preaches throughout the city preaching of peace, unity, tolerance and the destruction of the old ways of Chaos. This spreads like wildfire amongst the human race and the lower classes of the city causing civil unrest as the idols and images of the old Gods are questioned.
Fearing this could lead to their civilisations destruction, the humans are charged with heresy. Though instead of committing genocide on them (which would to further rebellion and disorders), the humans are forced into exile to barren wasteland of the southern desert. There they walked and dwelt whilst the Apostate sink into false comfort, thinking that their troubles are over. After years of suffering and death, the people lead by their prophet would reach the Southern Mountains. There it is said the great Demon Chaos, the enslaver and trickster of the desert people, came and tempted Tarsius. He was promised wealth and power over his wildest dreams in exchange for his obedience to the path of Chaos.. The prophet Tarsius would reject this offer, challenging the Demon King to a duel, winning as a flash of light descended from the heavens blinding the Demon King and dispelling his darkness. With their path cleared, they crossed the mountains and into a new land.
The humans would continue their mass exodus, led by their leader and prophet, until they reached they reached a river valley in the far north. They they settled, naming their new home Arkal, after the word in the Human Ancient Language meaning "water".