I'm afraid that the banjo information that has been passed down in respects to tuning and the origins of the 5 string are a bit ... well.... wrong.

The five string banjo can be found as early as 1790 and in the hands of black players, not white. The most likely African banjo ancester is the akonting, which has three strings (one noted and two drone) . Four strings seems to be the most comon way of finding early banjo images (pre- 1810) but these are mostly in the three long, one short, configuration.

The five string dessign we see today may have come from white players like Joel Sweeney, but more likely he did not invent or add the fifth string at all, he simply made that design famous. As far as early tuning went, that fouth string is tuned all the way down to a G. In the later tunings (1858 - 1880's) it would be an A. The viola tuning was not used until tenor banjos -which were not invented until 1914. The original (or at lewast oldest known tuning) was A F# D G D.