The spokesperson said the man was a 51-year-old Italian who underwent checks in the morning in Via della Conciliazione, a road leading up to the St. Peter's Basilica at the Vatican.
In a confrontation to disarm the man, one officer reported being lightly injury, police said.
The spokesperson added that there was no evidence suggesting the man was carrying the knife for terrorism-related purposes and he was arrested on charges of injuring and resisting an officer.
Ansa news agency reported that the arrested man suffered from a mental disorder.
(Reporting by Angelo Amante; Editing by Hugh Lawson)
