Concerns over Pope Francis' health have mounted in recent years as have questions about his succession. Here's what we know.

Pope Francis, who is in critical condition with a complex lung infection, offered his thanks for the "many messages of affection" he has received since he was hospitalized earlier this month. "I have been particularly struck by the letters and drawings from children,

Pope Francis, batting double pneumonia in hospital, remained stable throughout the day on Tuesday and did not have any new respiratory crises, the Vatican said. Francis, 88, had suffered two episodes of what the Vatican described as "acute respiratory insufficiency" on Monday.