This painting was bequeathed to the Museum by Alfred Stieglitz, whose "291" gallery in New York was the focus of early modernism in the United States. It was Stieglitz who gave Marsden Hartley his first one-person show in 1909 and helped finance his trip to Europe in 1912. There Hartley came into contact with the works of Paul Cézanne, Pablo Picasso, and Henri Matisse as well as German Expressionists such as Wassily Kandinsky and Franz Marc. Hartley made Painting No. 4 while in Germany at the outbreak of World War I. A part of his "Amerika" series, it combines the bright colors, flattened space, and simplified forms of French and German modern painting with symbols loosely drawn from Native American culture. While conveying Hartley's interest in representing spiritual values, the symbolism--such as the horse in front of the tepee flanked by plant forms--intentionally resists precise interpretation. In the face of his immersion in European modernism, his use of Native American motifs underscored Hartley's own American identity. He also spoke of the Native Americans as a gentle race, a counterbalance to European cultures preparing for a world war. John B. Ravenal, from Philadelphia Museum of Art: Handbook of the Collections (1995), p. 311.

An early work the artist painted during a stay in Germany from April 1914 to December 1915, Painting No. 4 (A Black Horse) is part of Hartley's "Amerika" series, which he began during the summer and fall of 1914. In these paintings Hartley incorporated motifs from Native American culture in order to evoke a uniquely American spiritual aesthetic, distinct from the African and Asian sources many of his European colleagues found compelling.

The black horse, bearing the number eight on its hindquarters, occupies the physical and symbolic center of this painting. Appearing in many of Hartley's paintings from this period, the number eight held universal mystical significance for the artist and also referred specifically to the eightpointed star he observed on royal and military insignia throughout Berlin. Hartley's incorporation of the number eight into his "Amerika" series suggests that his belief in abstract symbols was transcendently cross-cultural. The horse also appeared in Hartley's paintings of both German and Native American themes. Although the image of the horse and rider may have reflected those found in the paintings of his friend Franz Marc, it simultaneously represented the strength and grace of an animal popularly associated with Native American culture.

As in most of the "Amerika" series, in Painting No. 4 (A Black Horse) Hartley combined bright primary colors and simple geometric forms that extend out to the painted frame. Fish, birds, and flowering trees surround the black horse in an evocation of harmonious growth and fertility. Produced just as war was about to be declared in Europe, this painting and others from the "Amerika" series express Hartley's admiration and longing for a culture he perceived to be nobler and more peaceful. Twentieth Century Painting and Sculpture in the Philadelphia Museum of Art (2000), p. 46.