Pope Leo begins an ambitious 10-day tour of four African countries on Monday, urging global leaders to address the continent's needs, where more than a fifth of the world's Catholics live.
The first US pope heads to Algeria for two days before continuing on to Cameroon, Angola, and Equatorial Guinea on a whirlwind tour of 11 cities and towns, traversing nearly 18,000 km (11,185 miles) over 18 flights.
The pope is making the visit with a mission "to help turn the world's attention to Africa," Cardinal Michael Czerny, a senior Vatican official and close adviser to Leo, told Reuters.
The pope, who has emerged as an outspoken critic of the war in Iran, has made only one major overseas trip since being elected last May, visiting Turkey and Lebanon in November and December. He visited Monaco in March.
Leo, aged 70, relatively young and in good health for a pope, is undertaking one of the most complicated tours arranged for a pontiff in decades.
More than 20% of the world's Catholics live in Africa, according to Vatican statistics. The three sub-Saharan nations the pope is visiting have populations where more than half identify as Catholic.
Algeria, though, is an overwhelmingly Muslim country with under 10,000 Catholics among its population of some 48 million people. This is the first time it will host a Catholic pope.
Pope to give 25 speeches on a multitude of topics
Leo's tour is the 24th by a pope to Africa since the late 1960s.
He is expected to touch on many topics in 25 planned speeches over 10 days, Vatican spokesperson Matteo Bruni told journalists on Friday, given that the four nations face diverse issues.
Likely topics include exploitation of natural resources, Catholic-Muslim dialogue, and dangers of political corruption, said Bruni.
Cameroon and Equatorial Guinea have presidents who have been in power for decades and have been accused of human rights abuses, which they deny.
The biggest event of the itinerary will likely take place in Cameroon on Friday, when the Vatican said that some 600,000 are expected for a Mass in the coastal city of Douala.
Comfortable in several languages, Leo is expected to speak Italian, English, French, Portuguese, and Spanish during the trip.
Landing in Algeria in mid-morning on Monday, Leo will address the country's political leaders before visiting the Great Mosque of Algiers in only his second visit to a mosque as pope.
He will travel to Annaba on Tuesday, on Algeria's northeast coast, for a visit to the ruins of the ancient town of Hippo.
The site has special meaning to Leo, who is a member of the Augustinian religious order. The order is inspired by the teachings of fourth-century St. Augustine of Hippo, a major figure in the early Church.