The six Brandenburg Concertos BWV 1046-1051 , prized jewels of the world's musical heritage , were written in 1721 during BachÂ's appointment in Cöthen . Of the six works, Bach originally wrote earlier versions of numbers 1 and 5 which differ not only with regard to articulation but also at times different tones, different rhythms, instrumentation and of course form. These Urtext publications [BA 5201-BA 5206] taken from the New Bach Edition now give performers the possibility to play these earlier versions perhaps even along side the version known today.