The Díaz sisters played the marimba at the Papal mass in San Cristóbal de las Casas, Chipas, while people took communion.
The wood-planked instrument resembles its metal cousin, the xylophone. And nobody knows marimbas better than the four Díaz sisters, who began playing them in churches three decades ago at the invitation of the late Chiapas Bishop Samuel Ruiz, who tried to get more of Chiapas' heavily indigenous culture into the local churches.
The sisters have now been joined in the band by some brothers and other relatives.
Later in the mass indigenous children played violin while a ritual dance was performed.
The mass 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.
(With information from AP)