Ste. Trombetti has had more luck today, this time finding images of the vanished fountain that stood between the arch of Constantine and the Colosseum.
The first item is an undated photograph on a German site – the “- here. It’s quite a splendid image. The site owners seem to be demanding money, the thieves. So I won’t upload it here.
At Cultura Italia here is an interesting image of people digging around the base of the fountain. It’s by Pinelli Bartolomeo, “Escavazioni alla Meta Sudante”, and made in 1831. Unfortunately the site only makes this small image available, and I’m not at all sure about the accuracy of anything in the sketch:
Next, a photographic negative! Also at Cultura Italia, here. It was taken between 1880-1910:
And here, courtesy of Paint.Net, is a reversed, flipped, and auto-leveled version of the same:
It shows the water channel in the heart of the fountain.