Fugitive Mafia boss Matteo Messina Denaro communicates with henchmen using written messages buried in soil or hidden under rocks on sheep farms, investigators said.

The convicted Cosa Nostra boss also comes and goes from Sicily, possibly thanks to high-level protection, investigators added after detaining some of his alleged accomplices.

In early morning raids in the countryside of western Sicily, police took into custody 11 men investigators contend helped Messina Denaro wield power despite being at large since 1993.

Investigators described how Messina Denaro, 53, disdains telecommunications and relies on handwritten notes, or "pizzini", to relay orders.

The notes were wadded tight, covered in tape and hidden under rocks or dug into soil until go-betweens retrieved them. The messages were ordered destroyed after being read.

Messina Denaro was convicted in absentia as a mastermind of 1993 bombings in Rome, Florence and Milan. The attacks were aimed at intimidating investigators after "Boss of Bosses" Salvatore Rina was arrested in Palermo following two decades as a fugitive.

Since the 2006 arrest of Bernardo Provenzano, after 43 years in hiding, Messina Denaro became the most-wanted Mafia chieftain.

Police used eavesdropping devices and video cameras hidden in trees near farmhouses to help discover the message-delivery system.

Prosecutor Teresa Principato told reporters in Palermo that Messina Denaro sometimes "leaves Sicily and even Italy".

How he eludes capture is not known but "after so many years, and constant, punishing (investigative) work, he clearly enjoys some very, very important protection".

Mobsters young and old are loyal to Messina Denaro thanks to his generations-bridging "charisma", Palermo police official Rodolfo Ruperti said.

In 2013, the fugitive's sister was arrested, suspected of running extortion rackets for her brother.

Infiltration of public works contracts remains another Sicilian Mafia revenue source, after mainland 'Ndrangheta mobsters started dominating cocaine trafficking.

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