Johann Sebastian Bach's Brandenburg Concertos are some of the most important Baroque compositions written. They are actually a collection of ideas that Bach composed over a ten year period while he was a church musical director at Köthen, Germany.
They are all written in concerto grosso form and have the unofficial title of 'six concertos for several instruments'. Although the concertos were written across a number of years, they were finally completed in 1721.
On completion, Bach sent his work to the Margrave of Brandenburg in the hope that it would lead to further employment. Unfortunately, there is no record of a reply from the Margave, which could mean that he did not employ Bach.