The date of composition here is uncertain, though the high quality of the work suggests Bach had already attained a mastery of the fugue form. Thus, it probably dates at least to the early years of the composer's Weimar period (1708 - 1717), during which he was the court organist in the service of the Duke of Sachsen-Weimar. In this Fugue in B minor, he uses a theme by Italian composer Arcangelo Corelli, who gave it a vigorous (Allegro) treatment. Bach, on the other hand, slows the tempo and imaginatively alters its character, converting its vivacity to a slightly melancholy deliberateness. Bach presents Corelli's theme in a somber dressing at the outset, the pacing leisurely, the textures light. There is virtually no hint of the Italianate character or lively manner of the original here. Instead, the music has a serious demeanor, but is hardly devoid of color and spirit. As the work proceeds, inner voices become more active, textures thicken, and a subtle sense of tension develops, culminating in an ambivalent but resolute ending. Bach's fugal writing is brilliantly crafted throughout, growing somewhat more animated in the brighter second half. This fugue typically has a duration of six or seven minutes.