Gazetteer: The Duchy of Mar

From the introduction:

The prehistory of Mar is marked by the ancient civilization of Rhyta. A race of unknown origin, sages believe the Rhytians developed strange new forms of magic, conducted magical experiments on beasts, and used their arcane knowledge to command the elemental forces of nature. Sages also speculate that the Rhytians angered their gods who destroyed their civilization in a great cataclysm that swallowed entire cities into the earth. All that remains of their culture today are half-worn runes etched on half-buried columns of stone.