The Esper Saga
The Ancients is the name used for a great civilization that existed during the First Age. Little is known about them to modern savants, though it is apparent that they worshiped the Espers and had a much closer relationship with them than the peoples of the modern age, given how they built great wonders and channeled Magi far more expertly than later civilizations.
The Ancients were destroyed in the Kardus War. Most of their cities were rebuilt and claimed by other peoples, but a great deal of their greatest wonders have fallen into ruin. The Ancients designed the Warp Zones, and they were also responsible for the great underground network of Gargantuan transport tunnels. Besides these accomplishments, they were among the first to design advanced Magitech, and many scientists still study their designs and machines.