Ever since Ra's Al Ghul was introduced on Arrow, there has been discussion about the one thing most closely associated with him, the Lazarus Pit. Many say it won't appear on Arrow the way it does in the comics because Arrow is more grounded in reality and the thought of a magical pit that raises the dead is too out there. Others say it will definitely be on the show because in the few appearances we've seen Ra's, he's made mention of things that could only have happened if he was immortal. I have another theory I'd like to throw into the mix. The Lazarus Pit is a deception and Ra's is not immortal.
While [Arrow](series:720988) has ventured into some areas that are more unbelievable, they can mostly be explained without taking the leap into super-powers (Mirakuru as a powerful steroid, the Atom suit as advanced technology). But having an ancient spring that grants eternal life would be taking it a step too far. But Ra's Al Ghul's story can be explained even with that. The pit does not grant immortality. It has advanced healing properties but cannot grant immortality. So how do you explain Ra's' long life? Easy. There is more than one Ra's Al Ghul.
Ra's Al Ghul is not one man, but rather a lineage that is passed down through generations. Ra's Al Ghul is not a name, but rather a title, The Demon's Head. Whenever one Ra's feels it is time to step down, he finds a successor to pass the mantle onto and trains him to be the new Ra's, much like the Dread Pirate Roberts in The Princess Bride. He will impart the history and stories onto the new Ra's to use as his own backstory to heighten the legend. So, while this incarnation on Arrow appears to be immortal, he is just the current Ra's in a long line of them and wants Oliver to be the one to take his place.
Let me know in the comments below what you think. This is my first post so don't be too brutal!