Italian architect Stefano Boeri last week suggested that authorities use oak trees and flower pots at major sites to limit the impact of attacks using vehicles in big cities.
Boeri, the Italian creator of China's vertical forests, called for Italian cities to install trees in large pots - up to three metres wide - as barriers at key pedestrian sites.
After Bari and Florence, Rome is the latest city to see the proposal blossom.
Forty large pots containing oleander flowers were placed around the perimetre of Piazza del Quirinale in Rome, an official residence of the Italian president, reported Il Messaggero.
The concept is growing on others too.
"It's a way not to militarize our urban centres while making them greener," said Antonio Decaro, mayor of Bari, a city in southern Italy, cited in Corriere della Sera.
Decaro also said he wanted to involve students from Bari's Fine Arts Academy, who could decorate the large pots in order to create "the best response to extremism".
Leoluca Orlando, the mayor of the Sicilian capital Palermo, has also pledged to unite an alliance of creatives to design pots for his city.
And companies from the private sector could help foot the bill. Alessandro Mezzalira, president of construction firm Fitt Spa, says his company will donate "a considerable amount" to make it happen.
Mezzalira has called for others to contribute too. "The more we are, the better," he told Corriere della Sera.
Boeri, the architect behind the idea, had said that "we should oppose the instinct of death brought by these bestial people with the calm presence of plants – in particular oaks."
Milan has also chosen to reinforce security at several monuments with barriers made of concrete after the August 17th terrorist attack that killed 16 people in Barcelona.