"Vespers of 1640" at Church of St. Jean Baptiste The soprano Jolle Greenleaf and the violinist Scott Metcalfe may not have fully realized that they were on to something big when they started the Green Mountain Project, an outgrowth of Ms. Greenleaf's superb vocal ensemble, Tenet. The idea was to assemble the proper forces for Monteverdi's Vespers of the Blessed Virgin - a collection of sacred works published in 1610 - and to ring in 2010 with a performance celebrating the 400th anniversary of the work. The concert proved a resounding success, and Ms. Greenleaf (the group's artistic director) and Mr. Metcalfe (its music director) reconvened their forces at the start of 2011 and attracted a huge audience. Ruby Washington/The New York Times Vespers of 1640 The program, by the Green Mountain Project on Tuesday evening, was performed at the Church of St. Jean Baptiste. The tenor Zachary Wilder, accompanied by Hank Heijink playing the theorbo. They could easily have made it an annual outing, a New Year's counterpart to the Christmas season's "Messiah" performances. But this year they upped the ante by posing a question that seems simple after the fact but is actually the kind of inventive leap that gives rise to great programming ideas. What, they wondered, would a Monteverdi Vespers service have sounded like in 1640 - the year he published "Selva Morale e Spirituale," a sublime compilation of sacred works that includes a Mass, two Magnificats and several Psalm settings? The ensemble offered a consistently satisfying answer on Tuesday evening at the Church of St. Jean Baptiste, as part of Trinity Church's "Twelfth Night" Festival. As it had done with its performance of the 1610 Vespers, the group settled on a particular occasion - the Feast of the Immaculate Conception (celebrated on Dec. 8) - and selected the proper antiphons, to be chanted throughout the service. As a dramatic touch, a quintet performed the antiphons from positions all around the church, eventually joining the rest of the singers for the closing section, the antiphon "Conceptio tua, Dei Genitrix Virgo" and a 14-voice Magnificat by Giovanni Gabrieli. Did I say Gabrieli? As it turned out, the Green Mountain solution requires an asterisk, but only if you cling to the modern notion of a musical work having a single composer. That was not necessarily an issue in the more practical world of church music. In any case, building a second all-Monteverdi Vespers service proved impossible. Though he composed ample sacred music in his capacity as maestro di cappella at the Basilica San Marco, in Venice, he never published another complete Vespers. The Psalms from "Selva Morale" are a start. Other collections published between 1618 and 1650, along with a "Laudate Pueri" that survives only in manuscript and an "Ave Maris Stella," borrowed from the 1610 sequence, filled most of the gaps. Still, a few necessary movements remained elusive, and Ms. Greenleaf and Mr. Metcalfe filled the gaps with a motet, a Magnificat and a pair of instrumental works by Gabrieli, and a rich, contrapuntal setting of "Domine ad Adiuvandum" by Chiara Margarita Cozzolani, a singer, composer and Benedictine nun. The ensemble of nine voices (with the antiphon singers when larger forces were required), three violins, two cornettos, five sackbuts and continuo (a chamber organ and two theorbos) was split into two groups, deployed on either side of the organ to approximate the spatial effects for which San Marco and its composers were known. The singers and players produced a glorious, smoothly blended, beautifully textured sound. At first pulling this project out of the shadow of the 1610 Vespers seemed a steep challenge. After all, it is hard to match the vibrant opening of the earlier set, a reconfigured version of the Toccata from "L'Orfeo," overlaid with a choral setting of "Domine Ad Adiuvandum." But in an inspired move the ensemble drafted one of Gabrieli's best-known works, the antiphonal Canzon Septimi Toni, as a prelude. You quickly gave up comparing the two Vespers and accepted the update. Highlights were plentiful. In a supple rendering of "O Quam Pulchra Es" the tenor Zachary Wilder often seemed to be tailoring his phrasing to take advantage of the church's vibrant acoustics, and Sumner Thompson matched the passion of Mr. Wilder's performance in a strong account of "Salve O Regina." Ms. Greenleaf and Molly Quinn played off each other beautifully in the soprano duets, "Sancta Maria, Succurre Miseris" and in "Laetatus Sum," in which they were joined by a male trio - Jason McStoots and Marc Molomot, tenors, and Jesse Blumberg, baritone - that projected the text with power, clarity and warmth. But the real joys were in the choral pieces, most notably in the cascading counterpoint of the "Dixit Dominus" and the exquisite, painterly setting of "Nisi Dominus," with its alternation of brisk, rhythmic writing on the word "surgite" ("rise") and slow, descending, dissonances on the phrase "Qui manducatis panem doloris" ("You who eat the bread of sorrow"). And if you spent the evening wondering why the ensemble had not chosen a Monteverdi Magnificat to close on, the intricacy and sheer beauty of the Gabrieli setting answered that question decisively.