It is hard to think of a piece of music that has the mystique of The Chaconne (from the Partita No. 2 in D minor for solo violin). It has been admired, wrestled with, analyzed and arranged for the better part of two centuries, and the fascination with it seems only to be increasing.

The piece that composer Mario Castelnuovo-Tedesco called "the single greatest piece of music ever written" started life as the final movement of Bach's second Partita for unaccompanied violin, one of three partitas and three sonatas in a manuscript dated 1720.

The sonatas and partitas are technically difficult and musically challenging, and there has been much speculation about why he wrote them. The simplest answer, if not necessarily the right one, is that he wrote them for himself. He was an accomplished player, serious enough to own a violin by Jacob Stainer, the violin maker of the day, whose instruments were preferred to Stradivari's.

Polyphonic music for unaccompanied violin was not new in 1720, and was particularly common in Germany, perhaps because German violin virtuosos were a contentious and prickly lot, and some of them may have lacked friends. Heinrich Biber's Passacaglia, composed before Bach was born, is a large-scale set of variations on a ground bass, like Bach's Ciaccona, and is sometimes cited as a precursor, or even a model, for it. We don't know whether Bach knew of Biber's unpublished Passacaglia, though he likely knew of Biber.

The chaconne form had gone through several incarnations in its history by the time Bach turned to it. It already bore little resemblance to the original lively Spanish song and dance from about 1600, or to "La Ciaccona," a bass pattern and chord progression based on the song that crops up constantly in Italian music of the early 1600s. By Bach's time the archetypal "chaconne" or "ciaccona" was a set of variations in triple time over a recurring descending bass line, based on a theme that usually had a pronounced accent on the second beat. Bach actually begins his ciaccona on the second beat of the measure. The chaconne structure was remarkably flexible, and it shows up frequently in French ballets, suites for solo harpsichord, lute and guitar, and even in vocal music.

Bach's Ciaccona (he used the Italian name) contains the descending bass pattern 64 times, typically in sets of two, so it is, more or less, 31 variations on an eight-bar theme, though the divisions between one variation and another can be as indistinct as they are unimportant. The bass line and harmony are often changed beyond recognition, and there are several dramatic shifts, notably from D minor to D major, and later back to D minor. There was nothing unusual about this sort of loose treatment of the chaconne form. What makes Bach's piece unique is the depth of invention and the intensity of the musical ideas.

When the Bach revival began in the 1830s, the Chaconne caught the particular attention of musicians, many of whom thought that it was too small to be so big. It has been rearranged and transformed more times than Michael Jackson's face: Mendelssohn and Schumann both added piano accompaniments, Brahms wrote a version for piano left hand, and Busoni wrote one for both hands. There are two-violin versions, guitar transcriptions, arrangements for orchestra by Leopold Stokowski, among others, and a host of other versions.

Transcribing or expanding the solo violin works did not begin in the 1800s. There are contemporary transcriptions of some of the accompanied violin works for lute, and Bach himself transformed the prelude from the E major partita into a large concerted movement for solo organ and orchestra in Cantata No. 29. A credible theory has it that the famous organ Toccata and Fugue in D minor was originally for violin.

This transcription of the Chaconne for cello quartet was done by the Hungarian-American cellist Laszlo Varga, from the period when he was principal cellist of the New York Philharmonic under Dimitri Mitropoulos and Leonard Bernstein. He formed the first cello quartet in the United States in the 1950s, spawning a worldwide movement of cello ensembles. Varga has taught for many institutions, and, of the quartet performing tonight, David Garrett studied with him at the University of Houston, and Gloria Lum and Jonathan Karoly studied with Varga at the Aspen Festival.

The Chaconne has lately added another layer of mystique with musicologist Helga Thoene's theory that it was written as a memorial for Bach's first wife, and contains musical and numerological references to that purpose. Two groups of prominent musicians have thought enough of the theory to produce recordings illustrating the idea (the first CD has languished in obscurity, but the second was a major international hit). Interest in it as a phenomenon, as well as a piece of music, shows no signs of waning.

-- Lawyer and lutenist Howard Posner has also annotated programs for the Los Angeles Baroque Orchestra and the Coleman Chamber Concerts.