A fairly common practice in the Baroque era was for organists to "borrow" and transcribe orchestral music from themselves or other composers to create spectacular organ solos. J.S. Bach adapted several works by Vivaldi-this particular transcription was originally for solo violin and string orchestra. The brilliant showy solo line interspersed with tutti sections lent itself well to the colours of the organ and now to the trumpet ensemble. This arrangement can be played in whichever key best suits the performers (D, C, Bb, etc) with the appropriate trumpets being used (Bb, A Piccolo, D, Eb).