Bill Monroe’s 1930s recordings with his brother Charlie have been unavailable for so long that it seemed reasonable to think they were of little significance. Wrong. The 60 sides recorded by the Monroe Brothers for Bluebird Records from 1936 to 1938 are forgotten classics of American music, and their reissue in four volumes, two of which are now available with two more on the way, is a significant event, something akin to Columbia’s 1961 release of Robert Johnson: King Of The Delta Blues Singers.

Volume Two, Just A Song Of Old Kentucky, contains 15 songs recorded in a warehouse in Charlotte, North Carolina, in 1936. Charlie played rhythm guitar and sang lead; Bill, eight years younger, played mandolin and sang tenor harmony. They were famous for their haunting gospel numbers (“What Would You Give In Exchange For Your Soul?”, “Drifting Too Far From The Shore”), but they also recorded many secular sides, some of which became country and folk standards (“Nine Pound Hammer Is Too Heavy”, “Darling Corey”).

What set the Monroe Brothers apart from other brother duets — and there were many — was their musical prowess and their tight, soulful harmonizing. Years before he would form the first bluegrass band, Bill was already playing his mandolin at blazing speeds, consciously imitating his favorite fiddlers. No one had ever done that before.

Even today, it’s something of a shock to hear their incendiary version of “Roll In My Sweet Baby’s Arms”, which later became a bluegrass standard. (Flatt & Scruggs recorded what is probably the best-known version in 1950.) If you were playing it on a turntable, you’d probably check the speed. Similarly, Bill’s piercing mandolin playing on “The Saints Go Marching In”, recorded two years before Louis Armstrong would turn the song into a jazz standard, is like an arrow pointing the way to rock ‘n’ roll.

Then there’s Bill’s high, clear tenor. You can’t help but feel a little sorry for Charlie when you listen to these recordings; he may be the lead singer, but his little brother’s powerful harmony voice steals the show.

Brothers have a way of getting on each other’s nerves, and Bill and Charlie were no exception. They had bitter fights, and after one particularly nasty quarrel, Charlie called it quits. Bill, of course, became the father of bluegrass; Charlie, too, stayed in the business, though his post-Monroe Brothers singing career is all but forgotten today.

More than just proto-bluegrass, the music of the Monroe Brothers stands completely on its own. It was muscular, fiery, and completely modern — nothing sissy about it at all. Even if Bill had never recorded another lick of music after 1938, his place in country music history would still be assured.