2400 A.D.

Reptite Timeline

-Dinopolis is pulled to the Keystone T-2 to serve as a counter-balance for 
Chronopolis's introduction to the past.
-We may infer that with the Dragon God, Dinopolis, and the moon suddenly
disappearing, the Dragonian society underwent perilous times. 

Keystone T-1

-In an experiment meant to conquer time, Chronopolis causes the Time Crash. The 
full effects of this Crash are unknown.
-Lavos, awakened by Zeal in 12000 B.C., becomes aware of the temporally
exposed Chronopolis and, through the Frozen Flame, pulls it back thousands of
years in an attempt to introduce a major influence in history to corrupt Crono's
quest.

From: Chronology