The 23-voice Harmonia Chamber Singers and their intrepid leader, Rob Pacillo, have a weekend ahead that spans the centuries.

Saturday morning, the group is singing at a special Latin "Rorate Mass" in historic St. Ann Church at Broadway and Emslie Street. The "Rorate Mass" is an ancient Advent tradition that originated 1,000 years ago and became popular in Germany, Poland and Lithuania. Honoring the Blessed Virgin Mary, it is traditionally celebrated in the morning, by candlelight.

Saturday's "Rorate Mass" will be by candlelight and is being celebrated in Latin by Father Secondo Casarotto, the pastor of St. Anthony of Padua Church. Harmonia will be singing Gregorian chant and polyphonic Renaissance music.

The "Rorate Mass" was offered last year in St. Ann's Church and proved popular enough to warrant a repeat celebration this year. In March, Harmonia performed Palestrina's "Pope Marcellus Mass" in the context of a Tridentine Mass at St. Louis Church. The turnout for that, too, was greater than expected.

"I don't know how much publicity it got, but people were drawn to it," Pacillo says.

Pope Benedict XVI has been encouraging a greater use of Latin and the sacred music of the past, easing the way to celebrations like this. Still, it is not every day Buffalonians get the chance to absorb the ambience of a Mass as it might have been in the Renaissance.

"These things aren't done very commonly," says Pacillo. "You want to see people come out -- whether the faithful or not -- to see and experience things that are rare."

Music includes Gregorian chant as well as an "Ave Maria" of Josquin des Prez; and Palestrina's "Alma Redemptoris Mater." The setting of the "Rorate Caeli," the Advent prayer that gives the Mass its name, is by Francisco Guerrero.

With two Christmas concerts, Harmonia zips back to the present day.

The group is singing a Dave Brubeck arrangement of "We Three Kings" and the entrancing "Lux Aurumque" ("Light and Gold") by the popular contemporary composer Eric Whitacre. The centerpiece is the challenging Four Motets For Christmas by Francois Poulenc.

Other selections are "carolers' choice." Pacillo simply asked the singers what they wanted to sing.

Many of Harmonia's singers grew up performing in the famed choirs of St. Paul's Cathedral, and so the concert includes some beautiful Anglican favorites, such as Herbert Howells' "A Spotless Rose" and music by British choral master John Rutter.

"I think it's a really nice mix," Pacillo says. "It shows our diversity."



Harmonia Chamber Choir Rorate Mass

WHEN: 10 a.m. Saturday, St. Ann's Church and Shrine, 651 Broadway


WHAT: Christmas With Harmonia

WHEN: 7:30 p.m. at St. Bernadette Church, 5930 South Abbott Road, Orchard Park; 7 p.m. Saturday at St. Joseph University Church, 3269 Main St. 10 a.m. Saturday

TICKETS: Free, $10 donation requested