Just Three Bs Of Art Music? No Way!: It's TEN
Hans von Bulow showed himself very provincial when he limited his 3 Bs to Germans of two centuries. I investigated the history and geography of Kunstmusik, and came up with this very cosmopolitan set of 10:
JS Bach of Germany
Bartok of Hungary
Beethoven of Germany
Berlioz of France
Biber of Bohemia
Boccherini of Italy
Brahms of Germany
Britten of the UK
Bruckner of Austria
Byrd of England
The sacred music that Biber wrote for the Prince Archbishop of Salzburg greatly influenced that of his future successors, Mozart and Michael Haydn.