(Excerpt) Halfway through the Green Mountain Project’s Monday performance of Claudio Monteverdi’s “Vespero della Beata Vergine,” as Jason McStoots and Owen McIntosh virtuosically tripped through the echoing angelic lauds of “Duo seraphim,” Brian Giebler sidled in at mention of the Trinity, and the song coalesced into triadic solidity. It epitomized the music’s palpable architecture. Monteverdi historically straddled a shift in musical thought, from horizontal counterpoint to vertical harmony. One could hear ideas that once would have made Renaissance waves being stacked into pillars and vaults.