Nine citizens concerned about the climate emergency sat down holding banners on the Cavour, Umberto I, Vittorio Emanuele II and Principe Amedeo Savoia Aosta bridges.
One banner read: “Italy will be devastated by the climate crisis.”
“The politicians have abandoned us,” it continued.
Police intervened to end the protests after about 20 minutes.
The stunt is part of a long series of controversial acts of civil disobedience the group has staged to draw attention to the climate emergency.
Past instances include pouring easy-to-wash-off paint over the protective shields of artworks and famous monuments.
The government has moved to stiffen the penalties for such actions in a bid to discourage them.
This month, 12 UG members spent three nights in jail after blocking traffic on the highway to Rome’s Fiumicino airport.
“Today I’m here instead of being at university because I’m terrified, because we are facing the greatest catastrophe that the human race has ever experienced,” said Alessandra, a 21-year-old student who was among the protesters blocking the bridges.
“When worried people like me demonstrate peacefully, to remind their government to act, they get arrested.
“I am here today because I have hope that everyone can regain awareness of the power they have.
“Each of us can, and must, shout our dissent.
“The powers that be want us to believe that our individual voice is insignificant.
“But that’s only because they are afraid of what we can all do together.
“And that is why they are repressing us in an increasingly brutal, disproportionate way.”
ANSA