This 1961 Sotheby’s auction catalog describes the sale of Ruben’s 1603 painting, “Portrait of the Duke of Lerma on Horseback.” It is a fine example of an auction catalog, featuring color photographs of the original painting and black and white detail images. Background on the artist, the creation of the work, and the historical period which produced it are also provided, along with a list of previous owners, exhibition history, and a bibliography of scholarly works on the painting.