In his Violin Partita No. 1 in B minor (BWV 1002), Bach followed each of the usual French dance movements of the day (allemande, courante, sarabande and bourée) with a double. The double is a sort of variation that elaborates on the bass line of the previous movement.
Bach also broke with tradition in this partita by substituting the bourée in place of the typical Baroque gigue. Furthermore, he marked it Tempo di Borea.
Perhaps Bach was experimenting? Evolving? Rebelling? Whatever the case, his results are exquisite.
Hear for yourself in this performance by violinist, Gidon Kremer.