A day before Pope Francis arrived in the Mexican border city of Ciudad Juarez, a man who’d traveled from the south of the country said he saw the image of a crucified Christ in the clouds. “That kind of manifestation is rare these days,” he told El Diario, a Mexican newspaper, “even more so with the coming of the pope.” It was an auspicious sign for the faithful in a city that just five years ago was known for its gang killings and as the most murderous city in the world.

For three weeks, workers cleaned and painted streets in Juarez, and to ensure the city was on its best behavior, on Wednesday the local government suspended the sale of alcohol. The pope had originally wanted to cross the U.S.-Mexico border on his visit, an act he said would “be a beautiful gesture of brotherhood and support.” That turned out to be logistically impossible. Instead, Pope Francis dedicated much of his thoughts in Juarez to the plight of immigrants in a world increasingly shedding its borders for all but people.

“We cannot deny the humanitarian crisis which in recent years has meant migration for thousands of people, whether by train or highway or on foot, crossing hundreds of kilometers through mountains, deserts and inhospitable zones,” the pope said Wednesday. “The human tragedy that is forced migration is a global phenomenon today.”

Francis has made immigration one of the themes of his papacy. In his first official trip outside of Rome, he traveled to the migrant island of Lampedusa, off the coast of Sicily. There, he threw a wreath into the sea to memorialize the many North Africans who’d died crossing the Mediterranean in rickety wood boats, bound for Europe. “We have become used to other people’s suffering,” he said on his 2013 trip, “it doesn't concern us, it doesn't interest us, it’s none of our business.”

A year later, when he spoke to the U.S. Congress––the first reigning pope ever to do so––he said, “Let us seek for others the same possibilities which we seek for ourselves. Let us help others to grow, as we would like to be helped ourselves.”

The pope himself is the son of immigrants; his father was an Italian bookkeeper in Buenos Aires, and at the White House in 2015, he talked of the immigrant roots of his family, then added, “I am happy to be a guest in this country, which was largely built by such families.”

Juarez is one of Mexico’s best representations of why people emigrate. From 1970 to 2000, its population tripled. Factories drew low-skilled workers from across the country on the promise of jobs and money.

In Juarez, they worked 50-hour weeks that paid less than $5 a day. Little has changed since, and with a cost of living comparable to the U.S., poverty is endemic, helping Juarez become one of the deadliest cities in the world

In 2011, the city of 1.3 million saw about 10 homicides every day—many were victims of the warring drug cartels. But the casualties of this war were often the city’s poor. It’s believed nearly a quarter of Juarez’s population fled the violence––more than half to El Paso, Texas, its sister city across the Rio Grande. The city has since transformed itself: Crime has fallen dramatically, civic institutions have begun to function again, and Juarez welcomed the pope on Wednesday, on the final day of his six-day swing through Mexico.

Before he’d fly to Juarez, though, on Monday he stopped at the southernmost border, in the state of Chiapas, where, he spoke in the city of San Cristobal de las Casas, the epicenter of the 1994 Zapatista revolution. There, he told a crowd of mostly poor, indigenous people they’d been robbed by those “intoxicated by power, money and market trends.”

“Long live the pope of the poor!” the people chanted.

His trip from the the southern edge of Mexico, all the way to the north, in Ciudad Juarez, was seen by many as symbolic, a representation of the journey that many migrants make as they trek toward the U.S. In the finale of his six days in Mexico, Francis stopped at a prison in Juarez, then at college he spoke with workers and business leaders. Talking to the group, he condemned excessive capitalism.

“God will hold the slave drivers of our days accountable, and we must do everything to make sure that these situations do not happen again,” he said. “The flow of capital cannot decide the flow and life of people.”

Later, at the edge of the Rio Grande, he walked onto a newly built memorial dedicated to the immigrants who’d died crossing the border.  The long structure gradually rose to a view of the U.S., with an enormous cross jutting from the floor. Francis crossed himself and prayed. Across the river in El Paso a sign read “Immigrant Lives Matter.”

His last event in Mexico was a mass at the Ciudad Juarez Fairgrounds, where more than 200,000 people from both sides of the border listened. Speaking at the Mass, Francis said: “This crisis, which can be measured in numbers and statistics, we want instead to measure with names, stories, families.  They are the brothers and sisters of those expelled by poverty and violence, by drug trafficking and criminal organizations.”

The pope also paid tribute to migrant-rights activists, calling them “prophets of mercy” and the “beating heart and the accompanying feet of the Church that opens its arms and sustains.”