The divers braved the cold but sunny weather in nothing but a swimming costume, jumping off the Cavour bridge in the centre of the Italian capital into the waters below.
They were pulled to safety on to a waiting inflatable boat before joining the crowds on the river banks to celebrate.
The temperature of the water was no more than six degrees Celsius.
The oldest of the team was 66-year-old Maurizio Palmulli, also known as Mister Ok, a former lifeguard who was making his 31st dive.
“It was good and cold, friends! Really cold!” he told AFP after emerging from the river.
“Everything went well, no one got hurt, there were only nice folk and that makes me really, really happy,” he added.
The other divers were Marco Fois, Simone Carabella and Walter Schirra, who leapt from the bridge with an Italian flag in each hand.
Palmulli and his colleagues are continuing a tradition first practised in 1946 when the Italo-Belgian diver Rick de Sonay dived into to the river.