The Forgotten Age
Little is known about this period of time. The people who survived the Fourth Umbral Calamity placed the blame for the disaster solely on man's lust for knowledge. It was deemed that searching for answers to questions beyond the ken of mankind was sinful, and best left to the gods. Higher knowledge became outlawed as books and technologies were destroyed, surviving buildings were buried, and learned men were killed, bringing the progression of society to a firm halt. Civilization entered into a dark age comparable only to the religious zealotry of the Second Astral Era. Man's faith, and more importantly, his fear, was placed back in the unseen gods, with religious leaders once again rising to positions of unparalleled power. Stories of the Allagan Empire were reduced to mere allegory or narrative devices to teach children the sins of hubris.
The clergymen, wanting to ensure their rule over the people, manipulated any and all knowledge that made its way to the people, and introduced a specialized alphabet taught only to those of the cloth, so as to further raise themselves above the populace by ensuring their illiteracy. Ironically, following the Fifth Umbral Calamity, this alphabet would serve as the basis for the modern day Eorzean Alphabet.
This way of life continued on for over fifteen hundred years, until the passing of some unknown event triggered the Calamity of Ice, ushering in an endless winter of raging storms and freezing temperatures. Without the ability to grow crops and harvest, a massive majority of the population perished. The realm became so frigid, even the seas surrounding Eorzea froze over. As a positive to this, it did allow for the migration of the Miqo'te people, children of the ancestors who were driven to Ilsabard by the Allagan Empire.