Rome, February 11 - Failing strength rather than depression or any other illness dictated Pope Benedict XVI's decision to quit February 28, Vatican spokesman Federico Lombardi said after the shock announcement Monday. The 85-year-old pope "was absolutely not depressed, he had spiritual serenity and command of his relations with others," Father Lombardi said. "There was no illness which influenced his decision. "His strength diminished over the last few months. We know how old he is and that it is normal for people of advanced age to experience a decline in their strength. "The pope felt it in the last months and recognised it with lucidity".