I have heard that the string on the banjo that was added last was the lowest string the C or D depending on the tuning you use for home base. The african instrument which the banjo came from was one which specifially had that high rhythm string thang going on. It was the white folks who felt the need to civilize it and tune it like a viola. Which is where the tenor is located traditionally. This would naturally make it easier to find music to read. But I always love what "Pete" said in his book. " There ain't no notes to a banjo, you just play it".
The banjo is a wonder and a real good m usical partner. Theres always so much music ther to surprize and delight you. And, you can play it laying down.