… When Bach asked a violin to sound like a harpsichord.
The Sonatas and Partitas for solo violin (BWV 1001–1006) are a set of six works composed by Johann Sebastian Bach. They consist of three ‘church’ sonatas and three partitas (i.e., suites) completed by 1720, during the same period that also produced the Six Suites for Unaccompanied Cello and the Brandenburg Concertos .
JS Bach is famous for his lack of consideration of the human factor while composing, he was extremely demanding on his performers.. writing, for instance, cantatas where people were hardly allowed to breathe. Luckily, there has always been extremely talented musicians who brilliantly performed his pieces, to our great joy. The likes of Glenn Gould for the piano (harpsichord) pieces, Pablo Casals for the cello and Joseph Joachim for his (partial) recording of these sonatas, that were largely ignored before him, in 1903. The first recording of the complete set came 30 years later by Yehudi Menuhin .
When I first heard this sonata I could hardly believe that there was only one violin. Bach created an amazing piece where polyphony and counterpoint emerge, in such a beautiful and powerful way, from this small unaccompanied string instrument. A single violin that builds an incredible edifice of living complexity.
The first two sonatas and the three partitas of J.S. Bach’s six sonatas and partitas for solo violin make considerable demands on performers. However, the Sonata for solo violin No. 3 in C major, BWV 1005 is in a class by itself; it is so challenging a piece on every front that even the usually unflappable Jascha Heifetz used to break out in a cold sweat and suffer nervous bow-shakes when playing it, and it is a work of such consummate mastery, so perfectly planned and balanced, that any flaw in the performance sticks out like a sore thumb. In all fairness, Bach has gone beyond the bounds of reason in this grand Sonata—the violinist is asked to play music that might give a harpsichordist a headache 
The sonata consists of four movements ordered as slow-fast-slow-fast in tempo (as is generally the case): the first movement is an adagio. It is surprising in the way in unfolds… simple yet moving.
The first movement unfolds gradually from a single note with constant dotted rhythm in measured tread. The most strikingly progressive aspect of this Sonata is the use of key relationships to outline the large formal structures, while on a smaller level appearing to flaunt the traditional harmonic rules about related keys. After seven bars, for instance, we arrive quite naturally at the unrelated key of B major, and do not return to C major until the end of the movement. In the context of Bach’s time, the diminished seventh chords and other dissonances must have seemed dangerously anarchic, and even today the essentially non-functional treatment of local harmony makes the chords seem unexpected and new. 
Then comes the second movement; the fuga: The most impressive part of the sonata. It is also one of the longest fugues ever written and is notoriously difficult to play.
The glorious fugue which follows is at 354 measures Bach’s longest for any instrument or combination. It is a masterpiece of the highest order. Sustaining a large structure with limited melodic materials through long-range harmonic pacing is a characteristic technique of the Classical era, and this fugue shows that Bach understood it too. The subject is from a chorale, and is accompanied by a descending chromatic figure with just enough rhythmic variation at the end to be considered a countersubject. The fugue begins on the dominant, but as it moves to the tonic it turns unexpectedly away; the first cadence in C major comes only at the close of the exposition. A brief interlude leads to the second contrapuntal section, a fantastically inventive fragmentation of epic proportions, largely in minor keys. A longer interlude featuring an extended pedal point on D ends in a very satisfying G major cadence, and here Bach turns both subject and countersubject upside down to embark on an passage (marked al reverso) of aggressive, fearless polyphony, with harmonic rhythm twice as fast as the rest of the fugue, which verges on harmonic chaos. A reprise of the previous interlude leads to the dominant, and here Bach’s genius leads him to the perfect denouement – a literal repetition of the fugal exposition with but three changes – an extra voice in the first two statements, and an extra G on the last chord. This recapitulation, a formal idea which Bach had used in his e minor lute suite BWV 996, looks backward to the da capo aria form and forward to the classical style, and creates the huge arch which is responsible in large measure for the inexorability of this fugue. The number of elements Bach balances is absolutely staggering, and to describe the systems and construction patterns in Bach’s larger works hardly explains his genius. On the contrary, it makes even more extraordinary his ability to create such a balanced and interconnected whole. 
And finally the Largo and Allegro assai.
The Largo in F major which follows is a simple pastoral song showing Bach’s gift for continuous melody. It is the only slow movement in this set of six unaccompanied works which lacks a continuous rhythmic or dance foundation. This suggests the use of a quite free rubato based on the melodic and harmonic aspects of the piece. The final whirling Allegro assai shows how well Bach understood the instrument he was writing for. This is virtuoso music at its best. 
I leave you wit this performance of the Belgian violinist Arthur Grumiaux. A powerful and moving interpretation:
Bach – BWV 1005 C major sonata (II. fugue) – Hilary Hahn
Joseph Joachim plays Brahms Hungarian Dance No.1, recorded in 1903!
Wikipedia: Bach’s Sonatas and partitas for solo violin.
Recordings of Sonatas & Partitas in the 1950s.