Italian police have arrested 51 mafiosi accused of a running a crime empire from the coastal city of Ostia, just outside Rome.

About 500 security officers, backed by dog units, a helicopter and Swat teams, swept the Roman coastline in the largest anti-mafia police operation ever to be conducted in the region.

Police said that the arrested belonged to three spinoff clans of the infamous Sicilian Cosa Nostra and were considered the "Sancta Sanctorum" - Holy of Holies - of crime in the Rome area.

The Fasciani, Triassi and D'Agati families had struck a "pax mafiosa", police said, a deal to split the territory among themselves and run their criminal businesses in relative harmony with each other.

"No business was out of the gangs' control," police said, describing the number of charges brought against the arrested as "impressive".

Alongside traditional Mafia activities such as international drug trafficking, murder and extortion, the gangs ran a series of side businesses including beach umbrella rentals.

"The organisation had even infiltrated the local public administration to manage the allocation of council houses," police said.

Family boss Vincenzo Triassi was arrested with his wife on Tenerife, in cooperation with the Interpol.

A further 65 people, including local politicians, doctors, lawyers and entrepreneurs were arrested in a separate anti-mafia police operation in the southern town of Lamezia Terme.

"Italy is a seemingly democratic republic, based on organised crime's proceeds," said Roberto Saviano, the writer of the anti-mafia best-seller Gomorra.

Mafia Rome Ostia
Mafia gangs in the city of Ostia ran a series of side businesses including beach umbrella rentals on the Roman coastline (Reuters)