Board Thread:Questions and Answers/@comment-24550457-20140307163116/@comment-6554265-20140308082959

Ra's al Ghul, feeling bad for Batman's loss, stole Robin's corpse and threw it into the Lazurus Pit. The Lazurus Pit is a pool of mysterious liquids that completely heals anything that touches it. It also turns you into a young adult, explaining how Ra's has been living for over 600 years.