Keystone Dimension is the name given to the home dimension of the characters in Chrono Trigger. It is the reality that was created when Crono and his friends traveled through time and defeated Ozzie in the Middle Ages, subdued the Reptites in prehistoric times, thwarted Queen Zeal's plans, and defeated Lavos, thus preventing the Day of Lavos from coming to pass. This dimension was eventually split in two when Kid saved Serge from drowning in 1010 AD. In 1020 AD, when Serge uses the Chrono Trigger to save Schala from the Time Devourer in the Darkness At the End of Time, the dimensions are reunited once more.