Pope Francis has asked Mexican indigenous people in Chiapas state for forgiveness over they way they have been excluded from society.
He made his appeal while celebrating Mass in three native languages after a new Vatican decree approved their use.
The Pope also used the open-air service in San Cristobal de las Casas to warn about threats to the environment.
Throughout his five-day trip he has condemned the evils of forced emigration and drugs.
He has urged Mexico’s leaders to provide “true justice” to suffering citizens.
But on Monday he drew attention to the suffering of indigenous people in his address in Chiapas state.
“On many occasions, in a systematic and organised way, your people have been misunderstood and excluded from society,” the 79-year-old pontiff said after citing Popol Vuh, an ancient Mayan text.
“Some have considered your values, culture and traditions to be inferior. Others, intoxicated by power, money and market trends, have stolen your lands or contaminated them. How sad this is,” he said.
“How worthwhile it would be for each of us to examine our conscience and learn to say, ‘Forgive me!’”
Correspondents say that while Chiapas is the country’s least Roman Catholic state, tens of thousands of people attended an open-air Mass in a sports field in San Cristobal de las Casas.
Women wore colourfully embroidered dresses to deliver biblical readings and hymns in the Chol, Tzotzil and Tzeltal languages.
The pontiff highlighted the deep appreciation of indigenous people for nature and said their community had much to teach the rest of the world.
He also highlighted the need to care for the environment.
“We can no longer remain silent before one of the greatest environmental crises in world history,” he said,
While Mexico is the world’s second most populous Catholic nation after Brazil, only 58% are loyal to the Vatican in Chiapas in comparison to 82% in the rest of the country.
On Tuesday, the Pope heads to the capital of the western state of Michoacan, a region scarred by drug violence.
The Pope concludes his five-day trip in Ciudad Juarez on the US border, a city which has also been blighted by drug-related murders. A Mass there will highlight the plight of migrants.