The fresco features a majestic horse-like creature, known as hippocamp, gently carrying a beautiful female figure known as Nereid through the ocean waves. With her billowing garments and decisive grip on the steed’s muzzle, the Nereid seems to be holding on dedicatedly; her steed, his legs moving beneath the water, transports her with dedication. From a painterly perspective, this vignette is a multidimensional challenge and the artist has handled it exquisitely.

This remarkable artwork, a roman wall painting executed in encaustic on plaster, a very difficult technique, is at once a telling record of the technical achievements of the Roman artists, and an evocation of the beauty and delicacy of the mythological subjects that they often preferred in painting and sculpture.

Roman wall paintings were typically executed in fresco, the technique of painting tempera-based pigments over freshly prepared wet plaster. As the plaster dried and hardened, it solidified into a single painted surface, the pigments secured into the matrix of the dry plaster. The fresco technique allows the painter to work quickly and assuredly on the wall surface, with broad strokes of the brush.

However, this painting was instead executed in encaustic, a far trickier medium of pigments suspended in melted wax. Encaustic was commonly used in painting on wood, such as on the memorial plaques from Roman Egypt, but is exceptionally rare on a wall surface. Encaustic is thicker than tempera, a physically heavy medium that had to be applied in short, delicate brush strokes against the surface. On a wall, the heavy encaustic medium would tend to slide down since it was not immediately absorbed, smudging any delicacy in composition and technique. The painter of this vignette had to work with caution and assurance, defying the difficulty of his medium.

The motif or a figure riding behind a cow or a horse was common in classical mythology. Europa had her unwilling Jovian consort in the form of a bull, Glaucus had his sea-cow and Neptune had his assorted sea creatures, including the hippocamps (or sea-horses). The hippocamp was a creature with the protome of a horse and the rear of a fish, and in the myth, he was accorded the same stature of steed that fine terrestrial horses held. As such the hippocamp was the preferred ride of Neptune, the supreme god of the underwater world.
The nereids were of the same class as the sprites and nyads of the terrestrial forest and were the daughters of the terrestrial nymph Doris and the aquatic Nereus.

A comparable theme is shown in a fresco fragment in the British Museum, where Glaucus is riding a sea-cow. Though presented in tondo, this composition is close to our scene, showing a naturalistic blending of terrestrial forms and aquatic milieu. This painting is fairly accomplished, yet gives only a minimal sense of the transition from above-water forms to below-water forms. By comparison our encaustic fragment is a masterful display of technique-the human and equine torsos above water blend seamlessly to the limbs and billowing drapery that are indicated under the waves.

Related example: “Glaucus and the Sea-Cow” fresco fragment, British Museum, London.