Five large virtuoso keyboard fugues, each paired with a prelude or fantasia, stand apart from Bach’s early, generally shorter or more archaic works, and the later compositions that he gathered into the WTC and other collections. Among them is the Chromatic Fantasia and Fugue BWV 903, probably Bach’s best-known keyboard piece outside the great collections. With one exception (BWV 906), these pieces probably originated toward the end of Bach’s Weimar period (1714-7). Arguments have been made for placing BWV 903 at Cöthen (Stauff er 1989) or BWV 894 in the Leipzig period (Stinson 1989b) on the basis of notational evidence or patterns of manuscript transmission. But large display pieces like the Chromatic Fantasia might at fi rst have been withheld from circulation, serving as Bach’s private repertory for performance on special occasions. Eventually, however, these pieces-above all the Chromatic Fantasia and Fugue-circulated relatively widely and, unlike Bach’s earlier keyboard works, remained in use long aft er they had been composed. Th ere is evidence that Bach revised them later, at Cöthen or Leipzig, in one or two cases perhaps bringing together separately composed preludes and fugues. Th e later datings proposed for some of these pieces might apply to the revised versions.