An expert a cappella ensemble that has performed widely on three continents, Pomerium has recorded nine CDs, including four on Deutsche Grammophon. The bulk of their program this weekend presents music (by Josquin Desprez, Pierre de la Rue and others) from an early 16th-century manuscript devoted entirely to the Feast of the Seven Sorrows of the Blessed Virgin Mary; the second half offers later works dedicated to Mary by Tallis, Byrd, Palestrina, Lassus and others.

On November 12, the Paris-based Ensemble europ_en William Byrd, directed by New Zealander Graham O'Reilly, offers "The Path to Paradise," a program of French Baroque petits motets by Marc-Antoine Charpentier and his contemporaries for up to five voices.

The following Sunday, November 19, Trio Mediaeval, the all-female Norwegian vocal group touted as a successor to Anonymous 4, sings "Rose Window," a program combining music from the Middle Ages with traditional Nordic songs.

Music Before 1800's holiday offering will be "NoêŠl Nouvelet!" — medieval dances and carols from Spain, France, Germany and Britain performed by vocalists Jos_ Lemos and Danielle Svonavec and the five players of the Baltimore Consort.

On January 21, the Hilliard Ensemble will perform "In Paradisum," a program combining the Requiem Mass by Orlando di Lasso with motets on the themes of death and redemption by Palestrina. February 4 brings a recital by the Paris-based American harpsichordist Jory Vinikour featuring Bach's great Partita in D major and Handel's Suite in G minor and Chaconne in G major.

The most unusual offering of Music Before 1800's '06-07 season will be Tondal's Vision, a 12th-century music-drama from Dalmatia (present-day Croatia) about an unconscious knight whose soul leaves his body. Performing will be the six female singers of Dialogos, a medieval ensemble directed by soprano and chant scholar Katarina Livljanic.

Following a hiatus for Lent, Music Before 1800's final concert of the season, on April 22, features the resident professional choir of Corpus Christi Church (the series's venue) in an afternoon of sacred music from Rome ca. 1550-1650, including motets by Palestrina, Marenzio and de Monte as well as Carissimi's famous oratorio Jephte.

All Music Before 1800 concerts are on Sundays at 4 pm at Corpus Christi Church (529 West 121st Street, between Broadway and Amsterdam Avenue) in Manhattan. For more information, visit www.mb1800.org.