J.Pope-Hennessy, Italian High Renaissance and Baroque Sculpture, London and New York, 1970, pp.120-121, 420, fig.169.
The present piece is based on the Fontana delle Tartarughe in the Piazza Mattei in Rome. It was commissioned in 1581 by the Diputati sopra le Fontane, with Giacomo della Porta responsible for the design and Taddeo Landini for some of the execution, at least the figures. The turtles, from which the name of the fountain derives, were added in 1658 (op. cit., p.420).