MILAN - Anti-mafia prosecutors claimed a major victory over the powerful and growing 'ndrangheta crime syndicate, infiltrating intimate weddings, baptisms and other events to gather information that led to the arrests Tuesday of 305 people, including top bosses, and the seizure of more than 76 million in cash and property.

One of the most significant revelations to emerge from the investigation was that the Calabrian mob had a tight hierarchal structure like that of the Sicilian Mafia, and wasn't just an association of clans as previously believed. While expanding its economic reach into the wealthy Lombard region in northern Italy, the' ndrangheta is also concentrating its power in its native Calabria, exerting tight control over all strategic decision-making, anti-mafia prosecutors said.

The operation began before dawn with the 4 a.m. arrest of Domenico Oppedisano, the crime group's top boss, in the small coastal town of Rosarno in Calabria.

But the investigation owed its success to investigators' ability to infiltrate events like the 2009 wedding of the children of two crime bosses in Calabria, attended by thousands of well-wishers, where Oppedisano was named to his post, said Calabrian anti-mafia prosecutor Giuseppe Pignatone.

When Oppedisano was formally elevated some two weeks later, on Sept. 2, the feast of Madonna Polsi, undercover agents got video of the crime syndicate's major bosses all being confirmed in their new positions in the structure, he said.

"Police and carabinieri have been able to record since Aug. 1, 2009 all of the major negotiations of the various families," Pignatone told a news conference.

That includes some 40 similar meetings in Lombardy, which has become the Calabrian mob's moneymaking center, with operations focusing on excavations for construction sites, trash disposal and real estate. While officials seized 60 million in cash and property, prosecutors are unable to estimate how much the 'ndrangheta is cashing in each year.

Wiretaps indicate that as many as 500 'ndrangheta mobsters are operating in Lombardy, where 160 were arrested. They include Pino Neri, whom police said was in charge of the gang's businesses in Milan, where the 'ndrangheta has been making major inroads.

The investigation revealed the 'ndrangheta was extremely "hierarchical, united and pyramidal," and not just clan-based as previously believed, said Italy's chief anti-mafia prosecutor Piero Grasso.

That became clear when the Lombard branch, empowered by its riches, attempted to exert autonomy and was cut short when the Calabrian bosses sent a professional killer to murder the would-be upstarts, Pignatone said.

The 'ndrangheta has emerged as one of the most powerful of the crime syndicates, even if only since February has Italian law recognized it as a criminal organization. From Calabria, it has spread its tentacles to northern Italy, where it migrated in the 1970s and 1980s, to Germany, and as far away as Canada and Australia.