LEWISTON – The sounds of Gregorian chant will fill the Basilica of Saints Peter and Paul at 7 p.m. on the first Monday of each month, beginning Oct. 1.

“It’s not so much a concert as an entirely sung Mass,” said Scott Vaillancourt, music director at the basilica. “We did something similar this summer, and it was very well received.”

It is presented in an a capella setting and is referred to as “a dialogue,” he explained.

Vaillancourt said the Mass is almost entirely in English with some Latin. Known as the Rangueil Mass, it is the work of the Rev. Andre Gouzes, a Dominican priest who operates a liturgical center out of an ancient Cistercian Monastery in Sylvanes, France.

Such a Mass is “pretty unusual for this country,” Vaillancourt said. It also is celebrated in San Egidio in Italy as well as in Sylvanes.

Besides the Basilica choir directed by Vaillancourt, the entire congregation participates throughout the Mass. Parishioners are provided with the full music for the Mass and they sing all of the many responses and several prayers.

“This a very contemplative service,” Vaillancourt said.

He explained that much of the music is familiar to Catholics, but the singing of the choir will help to prompt them as the Mass proceeds.

The Rev. Robert D. Lariviere, rector of the basilica, will be celebrant for these Monday evening Masses.

Vaillancourt said the Gregorian chants are the oldest continually used music in the world. Legend says that Pope Gregory originated the chant in the early fifth century, but it has roots in pre-Christian Jewish chant.

It fell into disuse after the 1600s, but this ancient form of sacred music has undergone a popular revival in recent years.

“There are several different paths that chant has gone through,” Vaillancourt said, comparing the study of Gregorian chant to the field of archaeology. He said we don’t really know what the original chanting sounded like because early music notation was imprecise.

Vaillancourt said non-Catholics are invited to attend these special Masses.