The turtle fountain
is one of the prettiest fountains in Rome, built to a design by Giacomo Della Porta and with bronze sculptures by Taddeo Landini.
The fountain is located in the small Piazza Mattei
and is composed of four ephebes that push the turtles towards the upper tank to make them drink the fresh water of the ancient Aqua Virgo aqueduct, now called Acqua Vergine.
According to a popular legend, Duke Mattei, whose palace overlooks the square where the fountain is located, to convince his future father-in-law that he did not want to marry his daughter, organized a sumptuous party all night long.
The following morning, Mattei took his betrothed with his father to one of the windows of the building to admire the work done in one night. Later the window was bricked up so that no one could enjoy the same view anymore.
In reality the Duke Mattei, actually very influential, managed to have it built in the square in front of his palace, undertaking to pave the square and keep the fountain clean at his expense.
See a short video of the fountain: https://youtu.be/hCmrWCs3ZvQ