Gates of Elysium

The Gates of Elysium were an antimatter cascade, a pit of clashing realities. It was the location where Davros tried to kill the Nightmare Child during the Last Great Time War. Davros sent a distress signal to the War Doctor, who attempted to save him. Davros only wanted the Doctor to watch as the Nightmare Child consumed his command ship. (PROSE: The Third Wise Man)

The Tenth Doctor believed that Davros had been killed, however Dalek Caan had actually saved him, at the cost of his own sanity. (TV: The Stolen Earth)