Keyboard concertos by Johann Sebastian Bach soloists, were all adapted into harpsichord concertos by the composer, BWV 1058, 1054 and 1062 respectively. It is often assumed that Bach's extant violin concertos were written in his Köthen period (1717–1723): it can however not be proven from documentary evidence that any of them existed prior to around 1730. In September 1725 Bach performed organ music, accompanied by other instruments, in Dresden. The works he performed there have not been identified. More than a year later he composed several cantatas with an organ obligato part. Several movements of such cantatas were derived from earlier lost concertos, and resurfaced in
Brandenburg with Poland. Brandenburg originated in the Northern March in the 900s AD from areas conquered from the Wends, and later became the Margraviate of Brandenburg, a major principality of the Holy Roman Empire, with Albert the Bear as prince-elector. In the 17th century Brandenburg came under the rule of the House of Hohenzollern, the rulers of Prussia, who established Brandenburg-Prussia to become the core of the Kingdom of Prussia. Brandenburg became the Province of Brandenburg in 1815, a province within the kingdom and later within the Free State of Prussia. Brandenburg was established as a state in 1945 after World