The Fire Lake was very big because a volcano stood nearby. The constant volcano eruptions and spewing of fire from underground led to an overflow of lava on an otherwise empty plain. Slowly, the entire place became a lake of lava.
The few cities near the Fire Lake were all very famous because this place was exceptionally dangerous. Heaven Gods would surely die if they came to such a place. Even ordinary God Generals dared not come near. However, God Kings would often come to the Fire Lake to kill Chaos Beasts and obtain divine roots and battle merits.
Since fire spewed from everywhere, fire-elemental Chaos Beasts were very common in this area. Every one or two years, Chaos Beasts would be thrown out from underground by the underground fire. That ensured a never-ending supply of beasts in this area.