The extraordinary and unique colossus, constructed primarily of brick, stone and lava, was completed in 1580 and houses a series of small rooms beneath and inside it, including a grotto with a fountain where Francesco entertained guests. This composition is a dramatic re-working of a classical River God, usually shown lying down and supported on one elbow. The sculptor, Giambologna, would have been familiar with the numerous surviving examples from his intensive study of sculpture in Rome between 1550 and 1553, and again in 1572, when he was sent there by Grand Duke Cosimo I de' Medici, along with Vasari, and his fellow sculptor Ammanati.

A study of this piece can be found at The V&A, see below.