350 years of botany holds history of Roman monument.

Plants have been surveyed in the Colosseum since 1643. Credit: © alamy.com

The Roman Colosseum's history is stamped on its plants, say Italian researchers. In plant surveys spanning 350 years, they have charted the monument's progress from slum to tourist attraction, as well as Rome's growth into a metropolis and the city's changing climate.

Built in the first century AD, the Colosseum housed Gladiatorial combat until the sixth century. By 1643, when Italian doctor Domenico Panaroli compiled the first plant survey, the Romans had made themselves at home. "It was full of people living and working, and a hideout for thieves," says Giulia Caneva of the University of Rome.

Work on clearing the amphitheatre began in about 1810, under Napoleon's rule. There were three surveys of the Colosseum's flora in the nineteenth century, and one in 1951. Caneva and her colleagues did one more in 2001.

Such a wealth of data is almost certainly unique for a single site, says botanist Jim Dickson of the University of Glasgow, UK. "I find it hard to believe that anyone else has kept records for over four centuries," he says.

In total, the lists contain 684 species ? peaking in 1855, with 420, and declining to 242 today. About 200 of these were ever-present.

As the use of the amphitheatre changed, agricultural weeds gave way to opportunists associated with disturbed ground, Caneva's team has found1. There has also been a steady influx of exotic aliens.

This is what you'd expect, says Dickson. "There's more transport of plants now, deliberately and accidentally, than there's ever been," he comments.

“Rome was much colder and wetter in the seventeenth century Guilia Caneva , University of Rome”

The plant record also reveals a shift towards species that prefer a warmer, drier climate. This is partly due to Rome's growth, says Caneva: "The Colosseum used to be on the edge of the city; now it's in the middle."

It also reflects the warming of the climate over several centuries, and more recent climate change caused by humans. "In the seventeenth century, Rome was much colder and wetter," says Caneva. "The difference with today is too much to be explained by local change."

Historical naturalists' records, such as the timings of bird migration or flower blooming, are often the only way for today's researchers to detect the effects of climate change on wildlife.

References 1 Caneva, G. et al. The Colosseum's use and state of abandonment as analysed through its flora. International Biodeterioration and Biodegradation, 51, 211 - 219, (2003). Download references

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