For many centuries,
before being rediscovered by archaeologists and engineers, the Colosseum had been
overgrown with plants and trees. Many kinds of weeds could be found in the dark of the
arches or clinging to the top of the walls. Fig trees, elms, pear, olive and cherry trees
found their habitat in the amphitheatre, where sheep now grazed in the arena. 
Left: a vision of the Colosseum through the Arch of Constantine, by Canaletto. Click here to see the real perspective.
The arches and the ruins had become an enchanted garden full of flowers and greenery. Romantic travellers of the XVIII century found the Colosseum extremely suggestive, as if nature had again taken possession of the place. Models started to be made and sold all over Europe. Shelley, Byron, Dickens, Thomas Cole, Henry James and other innumerable artists fell in love with the fascination of the old, evocative ruins.
In the year 1727 formal permission was even granted to collect the grass and herbs growing inside the monument. The flora of the Colosseum has been scientifically examined in several botanical works (Sebastiani, 1815, Deakin, 1855). The latter study reports 420 different species of plants, and some specialists stated that some of the rarest species weren't to be found elsewhere in Europe.
Painters were especially fond of the picturesque aspect of the Colosseum. In Rome there has recently been an exhibition (Frondose arcate) on the image of the Colosseum as reported by the French painters Jean-Antoine Constantin and Francois-Marius Granet, who worked in Rome between 1777 and 1830.
It is interesting to read about the attitude of Granet when, on his return to Rome in 1829, visits the Forums and the Colosseum and is terribly disappointed by the work of the "engineers" who were cleaning and restoring the old stones, taking away the weeds and trees: "I was amazed that the Romans, who have such a taste in all things, could have allowed such a slaughter. Modern intervention has ruined those wonderful monuments". And on another occasion: "It has been Science and its cold rules that have reduced that place in such a state that the Art of painting cries".
