Brian Clarke’s Sienna is a series of paintings created between 1989 and 1990. The works are distinguished by their burnt sienna base, obtained through gestural washes of the natural earth pigment sienna, with its distinctive warm, reddish-brown color. The use of washes as an underpainting technique is characteristic of Clarke's practice during the late 1980s and early 1990s.

In the paintings from this series, the sienna ground is variably overlaid with lattice-like grids, calligraphic marks and computergram motifs. In The Least of These, Clarke also integrated a crucifix and horns into the composition.

These works are exemplary of Clarke’s interest in the rendering of flames during this period, a motif he also explored in his stained glass commission for the Holocaust Memorial Synagogue in Darmstadt.