The Neptune Fountain at the foot of the Gloriette hill was designed to be the crowning monument of the Great Parterre. Commissioned by Empress Maria Theresa, work on the fountain began in 1776 and was completed within four years, just prior to the death of the empress. The overall design was done by Johann Ferdinand Hetzendorf von Hohenberg; the marble sculptural group was executed by Wilhelm Beyer.

The retaining wall of the Neptune Fountain merges into the slope of the Gloriette hill and includes a balustrade adorned with ornate vases. From a projecting semi-oval plinth, a rocky formation emerges with the sea-god Neptune and his entourage. The plinth is segmented by panels decorated with masks and separated and embellished with garlands. Neptune stands atop the grotto at the center of the figure group in a shell-shaped chariot holding a trident. A nymph is seated to his left. The sea-goddess Thetis kneels to his right, asking the sea god to favor her son Achilles on his voyage to Troy.

Appearing at the base of the grotto are four tritons—creatures who are half-man and half-fish—who are part of the sea-god's entourage. Each holds a conch shell trumpet with which they can inspire fear. They are restraining the sea-horses who draw Neptune's chariot across the seas. This image of Neptune commanding the watery dominion was a common symbol in sixteenth, seventeenth, and eighteenth-century art, to represent monarchs controlling the fate of their people. In the nineteenth century, a bank of evergreen trees was planted behind the white figural group to provide a dark contrast.