Bach's six years as Kapellmeister to Prince Leopold of Anhalt-Cöthen (1717-23) witnessed the composition of a large proportion of his instrumental music, including his violin concerti, his sonatas for violin and cello, and the first book of the Well-Tempered Clavier. The six 'Brandenburg' Concerti also belong to these years, but they were not written for use at Cöthen (although they were doubtless performed there). As their name suggests, they were composed as the result of a commission by Christian Ludwig, Margrave of Brandenburg, whom Bach probably met while he was in Carlsbad in the summer of 1718. Bach did not complete the work until March 24th, 1721, however, when he dispatched his beautifully written manuscript score of 'Six Concertos for Several Instruments' to the Margrave's palace in Berlin. But by then his patron appears to have forgotten the interest which, according to Bach's own elaborately respectful dedication in French, he had taken 'a year or two ago' in the composer's 'insignificant musical talent', for the good condition of the score (which was sold in a job lot with a miscellaneous collection of music after the Margrave's death in 1734) suggests that it cannot have seen much service. It is ironical that Christian Ludwig's name should be remembered solely because of some music that he may never have troubled to listen to.
The 'Brandenburgs' represent the highest development of the Italian concerto grosso, of which the twelve works forming Corelli's Op. 6 (published c. 1713 but composed many years earlier) are among the most celebrated if not positively the earliest examples. It is on Corelli's plan, which relies for its effect on the contrast of a small instrumental group (concertino) consisting of two violins and cello, with a larger one (ripieno) consisting of the normal string orchestra, that most of eighteenth century concerti grossi (including Handel's set of twelve, Op. 6, composed in 1739) are based. But in Bach's set there is a variety and subtlety of instrumentation, both as regards the use of string and wind instruments, that is far in advance of even the less conventionally scored concerti of Vivaldi, Telemann or Handel and an originality of design coupled with a cogency of musical thought that has few parallels in the eighteenth century or, indeed, in more recent times.
Uncredited liner notes from Bach: Brandenburg Concertos - All Six Complete, Murray Hill Records #949865