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Pope Francis on Monday denounced the centuries-old exploitation and social exclusion of Mexico's indigenous people and said the world should instead learn from their culture and appreciation of nature.

The pontiff celebrated Mexico's Indians during a visit to the southern state of Chiapas, a center of indigenous culture, where he presided over a Mass in three native languages thanks to a new Vatican decree approving their use in liturgy.

In his homily, history's first Latin American pope melded two of his core concerns: appreciation for indigenous cultures of the Americas and the need to care for the environment.

"The environmental challenge that we are experiencing and its human causes affects us all and demands our response," Francis said. "We can no longer remain silent before one of the greatest environmental crises in world history."

"In this regard, you have much to teach us," he added, speaking under clear blue skies at a sports complex in the mountain city of San Cristobal de las Casas.

The soft sounds of marimbas accompanied the opening the Mass in front of a replica of the brilliant yellow and red facade of the Sans Cristobal de las Casas cathedral, which Francis was scheduled to visit later in the day.

Crowds chanted "Francis friend, San Cristobal is with you" as he arrived. Some 500,000 faithful were expected to see the pope in the city, including about 100,000 who gathered on the dirt field for the Mass.

The visit, at the midway mark of Francis' five-day trip to Mexico, is also aimed at boosting the faith in the least Catholic state in Mexico.

Francis has already issued a sweeping apology for the Catholic Church's colonial-era crimes against indigenous people in Latin America. On Monday he was celebrating their culture in ways the local church hierarchy has often sought to play down, in a clear demonstration of his belief that Indians have an important role to play in Mexico today.

"I ask you to show singular tenderness in the way you regard indigenous peoples and their fascinating but not infrequently decimated cultures," Francis told Mexico's bishops Saturday in a speech outlining their marching orders. "The indigenous people of Mexico still await true recognition of the richness of their contribution and the fruitfulness of their presence."

The Mexican hierarchy has long bristled at the region's "Indian church," a mixture of Catholicism and indigenous culture that can include pine boughs, eggs and references to "God the Father and Mother" in services. It was a tradition that was embraced by the late bishop of San Cristobal de las Casas, Samuel Ruiz, who ran afoul of both the Mexican church and the Vatican at times for his use of the local ways.

Worshippers began filing shortly after midnight into the site of the Mass, which included readings, prayers and hymns in the three main indigenous languages of Chiapas: Tzeltal, Tzotzil and Chol, which are spoken by just over 1 million people, according to Mexico's latest census.

The pope was presenting an official decree authorizing the languages to be used, some 50 years after the Second Vatican Council paved the way for Mass to be celebrated in the vernacular rather than in Latin.

Despite the pope's overture, residents of Chiapas said they believe Francis is coming mostly to confirm their faith, not their status as indigenous.

"It doesn't matter that I'm indigenous; I think it's more that I'm Catholic," said Emanuel Gomez, a 22-year-old Tzotzil who planned to attend the Mass. "The pope comes to encourage our hearts and faith as Catholics."

He added, though, that the visit would "lift us up so we don't feel scorned by the powerful and rich."

According to government statistics about 46 percent of Mexicans were living in poverty in 2014. That number surges in Chiapas, where some 76 percent were living in poverty, 32 percent in extreme poverty.

Francis has insisted that his is a "poor church, for the poor." After the Mass, Francis was scheduled to hear testimony from a handful of Chiapas families about the hardships they face.

"He comes to redeem an entire struggle by the people," said the Rev. Marcelino Perez, an indigenous priest who was charged with translating the homily into Tzotzil.

The pope has frequently expressed admiration for indigenous peoples, particularly their sense of custodianship of the environment. As archbishop in Argentina, he was heavily responsible for a major document of the entire Latin American church hierarchy in which bishops praised the harmonious way indigenous people live with nature.

Indigenous communities have legal rights to much of Mexico's forest and desert lands, and have long battled with outsiders to protect them -- and to share in the revenues they produce.

Mining and commercial logging interests that were granted concessions by national or state governments long denuded or polluted indigenous lands.

San Cristobal is home to two of the most famed religious defenders of indigenous people in Mexican history: Bishops Bartolome de las Casas in the 16th century and Samuel Ruiz, who died in 2011.

Both were beloved by indigenous people and widely reviled among the wealthy classes and much of the church hierarchy.

Many officials accused Ruiz of acting on behalf of the Zapatista rebels in their 1994 uprising for greater indigenous rights.

Part of the liberation theology movement that swept Latin America after Vatican II, Ruiz tried to fend off the rapid growth of Protestant denominations by adapting to indigenous customs.

One of his controversial measures was to rely heavily on married male lay workers because local culture granted more respect to men with children than to childless, celibate men such as priests.

Some in the church worried the married deacons were taking on priestly functions.

In 2002, under Pope John Paul II, the Vatican asked the Chiapas diocese to halt deacon ordinations. But under Francis, the ordinations were renewed in 2014.

In a sign that Ruiz remains a controversial figure, the Vatican declined to say whether Francis would pray at his tomb during his visit to the cathedral.

"There are many who feel he was more of a political figure than a religious one, often disregarding that the motivation for all that he did was Jesus Christ," Dorantes said.