Prom 72: Les Arts Florissants / Christie, Royal Albert Hall, London

A requiem by Marc-Antoine Charpentier? Granted, the rediscovery over the past 50 years of 17th-century France's greatest master of sacred music has yielded one Baroque treasure after another.

A requiem by Marc-Antoine Charpentier? Granted, the rediscovery over the past 50 years of 17th-century France's greatest master of sacred music has yielded one Baroque treasure after another. But where had William Christie and Les Arts Florissants found the unlisted Grand office des morts with which they opened their visit to this year's Proms - apparently dating from 1671-2 and running for no less than 56 minutes?

In fact, this proved to be a conflation, edited by John S Powell, of several sacred works marking deaths in the family of the young Charpentier's patroness Mademoiselle de Guise, comprising his Messe pour les trépassés ("Mass for the Departed") interspersed with a more dramatic "Dies irae" sequence, a motet "Miserere mei" expressing the plaints of souls in purgatory and a setting of the "De profundis" psalm.

Much of the music is fairly straightforward, even plain - Charpentier had only recently returned from his studies under Carissimi in Rome when he wrote it - and most of it is sombre, with even the "Sanctus" cast in the minor mode. Perhaps not even the peerless solicitude of Christie's singers and players could convince one that the compilation quite transcended the sum of its parts. But there were memorable stretches: the plangent cries of the purgatorial souls led by the tenor Paul Agnew; the tenderly contrapuntal "Pie Jesu" setting in the "Dies irae"; and, at the end of the "Agnus Dei", a wondrously yielding final "Dona eis requiem sempiternam".

The second half of this celebration of the tercentenary of Charpentier's death was altogether more cheerful, opening with the extraordinary Messe pour plusieurs instruments au lieu des orgues (1674). This was a unique take on the French organ mass tradition of plainchant interspersed with organ ritornellos. When a newly commissioned organ failed to arrive on time at a Paris monastery, Charpentier simply composed an equivalent set of pieces for orchestra, scoring them in an as organ-like a way as he could. Christie put his men up in the Royal Albert Hall gallery for the chants in the "Kyrie" and "Gloria", throwing the ingenious subdivisions and blends of Charpentier's orchestration into stronger relief. The "Sanctus", however, proved to be a substantial and purely orchestral movement of the most cheerful inventiveness.

And so to the flamboyant opening fanfares of the "Te Deum", so long familiar as the Eurovision signature tune and doubtless symbolising the Church Militant of the Jesuits for whom Charpentier probably composed it in the 1690s. As in the Messe pour plusieurs instruments, what his pointing of expression and colour suggested was how much of Charpentier's facility, even genius, lay in his gift for permutation - his skill in building forms from every possible combination.

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