Nine Real Sociedad fans were injured in central Rome during clashes with Lazio supporters on the eve of Thursday's Europa League match between the two teams, police said.
About 70 Spanish supporters were attacked by about 80 Lazio supporters in Via Leonina, near the Colosseum, at about 23:00 CET on Wednesday, a Rome police spokesperson said.
They used blunt objects and knives, police said, releasing a picture of weapons presumed to have been used in the attack, including a hammer, sticks and batons, wrenches and a chain.
The attackers fled as the police arrived, the spokesperson said.