Gates of Elysium
The Gate of Elysium was where the Doctor believed Davros had been killed when his command ship flew into the jaws of the Nightmare Child. This was during the first year of the Last Great Time War. The Doctor attempted to save Davros but failed. (DW: The Stolen Earth)
However, Dalek Caan was able to save Davros from being killed at Elysium by initiating an emergency temporal shift after an encounter with the Doctor. (DW: Evolution of the Daleks)
The shift allowed Caan to arrive just before Davros died and take him to another point in time and space. Dalek Caan lost his sanity as a result of interfering with the Time War, every detail of which is time locked. By saving Davros, Caan had ensured the creation of the New Dalek Empire. (DW: The Stolen Earth)
