Johann Sebastian Bach’s Concerto for two violins BWV 1043, or “The Bach Double” was written sometime around 1725 (the exact date is unknown). It was during the same period he wrote his famous Brandenburg concerti, during the time he was writing for Prince Leopold of Cothen and he had a good orchestra with two well-trained violinists at his disposal.
This is the middle movement, marked “Largo, ma non-tango”, or “Slowly, but not too much”. J.S. Bach wanted it to be expansive and expressive, but not slow down to a dirge. The bass line, in particular, is so expressive it’s almost melodic, but to the chagrin of cellos and basses everywhere, sadly not the mainline.