Pope Leo, a former missionary critical of the wealthy elite, visits Monaco with a pro-poor message, highlighting his first western European trip of his papacy.

Pope Leo heads on Saturday to the Mediterranean principality of Monaco, a millionaires’ playground on the French Riviera that is the pontiff’s surprise pick for the first western European trip of his papacy. The US-born pope, a former missionary critical of the wealthy elite, will helicopter in for a day in the world’s second-smallest state, best known for its casinos, luxury yachts and Michelin-starred dining. In Monte Carlo, billboards featuring mild-mannered, white-cassocked Leo stand in...