The rose window at St. John the Divine in New York.

One of the great achievements of the early music movement - and Martin Pearlman's Boston Baroque in particular - has been its reclamation of Monteverdi from his lapsarian status as "that Italian guy before Bach." Last weekend's performances of the great composer's Vespers of 1610 only cemented that achievement. Monteverdi should have always been set somewhere on the boundary of Big Three territory, in that he brought pre-baroque forms such as the madrigal to the highest pitch they ever reached. But as early music pioneers have made us more and more familiar with his masterpieces, his status as a forger of new musical form has begun to seem to rival Beethoven's and Wagner's. Monteverdi of course all but invented opera, but nearly as original is his Vespers, a work unprecedented (at the time) in its scope and ambition, and one that all but defies categorization even today.

Of course on the surface, Monteverdi pretty much follows the normal structure of the Catholic rite of vespers, the evening ritual in which a series of sung psalms and antiphons leads to a Magnificat, a canticle dedicated to both the glory and humility of the Virgin Mary. In fact the Vespers was written, many believe, as a kind of audition for the top musical post at St. Mark's cathedral in Venice (Monteverdi got the job).

But it's hard to look at this piece as a résumé-builder, even for a genius; instead it sometimes feels like a kind of musical big bang, a technical, stylistic, and metaphorical explosion that in a way kick-started everything. Monteverdi leaps from motet to sonata to psalm and back again, all while somehow maintaining a sense of unity; he splits and re-forms his choir at will, and sometimes provides them with up to 10 separate vocal parts, all operating in synchrony(the piece also calls for seven soloists). What's more, Vespers is set all over the performance space, be it cathedral, chapel or concert hall - sometimes we can't even see the singers, as they're intended as voices of the cosmos, responding re-assuringly to the profession of human faith.

Now I don't believe in God, but Monteverdi certainly did (he eventually became a priest), and frankly, sometimes he almost convinces me of His existence. There are few more haunting moments in all of Western music, for instance, than "Duo seraphim," his duet for two angels floating in space, singing the glory of the Almighty (they're eventually joined by a third, who fuses with them into a single note when they praise the Trinity). Here conductor Martin Pearlman placed his tenors, Derek Chester and Aaron Sheehan, in the balconies of Jordan Hall, to thrillingly plaintive effect, and Monteverdi's evocation of the mystery of God's presence gripped us not only as great music but also as great theatre (and maybe even great architecture).

Alas, not all the soloists fared as well from the stage itself. Mr. Pearlman had clearly instructed his singers to strip their styles down toward pure-tone singing, and so I missed some of the vocal richness I expected from Mary Wilson and Kristen Watson, who both shone to better advantage in operatic roles with Boston Baroque earlier this year; indeed, of Pearlman's soloists (almost all of them familiar from earlier programs) I felt only baritone Donald Wilkinson was operating at his best. And the wind section, though fine in unison, sometimes got a little ragged when each instrument was exposed for long stretches. Likewise the height of Monteverdi's polyphony - those 10-part-plus sequences - didn't always feel entirely coherent.

But this is, admittedly, an incredible challenge, and any roughness here may have been partly due to understandable opening-night coordination issues; at any rate the chorus generally sounded superb, and nowhere more beautiful than in Monteverdi's concluding Magnificat, one of the most touching ever written. And Pearlman's mastery of the total arc of the Vespers was always and everywhere evident. The piece calls for a high degree of editorial intervention; much of the instrumentation is suggested but not pinned down, the position of some motets is disputed, and precisely which antiphons should be included is never specified (Pearlman took his from the Feast of the Assumption, certainly an appropriate choice). It's no secret that Pearlman's decisions on these and other key points have led to a version that many consider "the" Vespers of our time (it's already won a Grammy). Certainly the "Pearlman version" limns every - sometimes contradictory - facet of the piece: its intimacy and its grandeur, its period "feel" and yet its strange sense of timelessness. His exploitation of every nook and cranny of Jordan Hall was also brilliant, and only makes me long to hear this version in New York on March 6, when Boston Baroque will bring the Vespers to the Cathedral of St. John the Divine, surely a close-to-ideal venue for hearing Monteverdi's music of the spheres.