Ranieri Adami Piccolomini slashed a 75-year-old pensioner in the throat in Piazza De Renzi, in Rome's central Trastevere neighbourhood, before punching a 52-year-old man, Corriere della Sera reported.
Piccolomini, named as a descendant of the 15th-century Pope Pius II, was arrested after the reportedly unmotivated attack.
The pensioner was taken to hospital with a wound just millimetres away from his jugular vein, a major vein which carries blood from the head.
Piccolomini has in recent years been implicated in a number of violent crimes, earning himself the ‘Black Count’ nickname in the press. He was tried and then acquitted for the 1996 murder of 23-year-old Paolo Segatori, who was stabbed 20 times, Italian media reported.
In April 2012, he was arrested for attacking a Bangladeshi man and breaking his nose, days after he was reported for attacking another three Bangladeshis, Roma Today reported.
Piccolomini was put under house arrest in 2011 for domestic violence and earlier this year was hospitalized after a fight in Trastevere, the news website said.