Nuns pray during a Roman Catholic service for Pope Benedict XVI at Berlin's St Hedwigs Cathedral February 28, 2013. Pope Benedict left the Vatican on Thursday after pledging unconditional obedience to whoever succeeds him to guide the Roman Catholic Church at one of the most crisis-ridden periods in its 2,000-year history. REUTERS/Markus Schreiber/Pool (GERMANY - Tags: POLITICS RELIGION TPX IMAGES OF THE DAY)