Unison passages

Julian Mincham wrote (November 10, 2006):
I have deleted the email so can't find the reference but I think someone asked about Bach's unison passages.

The earliest example I know of comes at the end on the 6^th movement of BWV 71 'God is my King' written for the Mühlhausen city council 1708. The last line of text is intoned on middle C in all four choral parts, moving to Db, C Bb and C for the final (original) cadence.