MOSCOW — It is unclear why they gathered. A police statement said it was to discuss “escalating problems of the criminal world.” Some insiders spoke of a conflict between Moscow crime bosses and of a looming underworld war reminiscent of the bloody battles of a decade ago.

Whatever the reason, when leaders of Russia’s criminal elite convened on a yacht in the Moscow River recently, the police moved swiftly to stop the meeting.

In black masks, with weapons drawn, commandos pounced from a hovering helicopter onto the roof of the yacht, starting a media frenzy when they briefly detained 37 men known here as Vory v Zakone or “thieves-in-law.”

A Mafia-like caste forged in the Soviet gulag, the Vory v Zakone maintain a hallowed place in Russia’s criminal lore, something akin to the notorious Five Families in the annals of New York crime.

Though the Vory’s influence appears to have waned, Russians have long had an affinity for the group, perhaps because it has come to symbolize opposition to the country’s often arbitrary political and legal practices, academics and other experts say.

After the Soviet Union collapsed, the Vory v Zakone “hit platinum,” said Andrei D. Konstantinov, a journalist and novelist who has written about criminal subcultures. “Everyone started to sing about this topic, to talk about it, to make television series, write books,” he said. “It became fashionable.”

In the last 15 years the Vory have spread around the world, from Moscow to Madrid to Berlin and Brooklyn. They are involved in everything from petty theft to billion-dollar money laundering schemes, while also acting as unofficial jurists among conflicting Russian criminal factions.

Born of Stalin’s prison camps, the Vory grew into criminal barons that kept order in the gulags and governed the dark gaps in Soviet life beyond the reach of the K.G.B. While the Communist Party held a steadfast grip on government and society, they had something of a monopoly on crime.

With their own code of ethics, hierarchy and even language, they formed a society in opposition to rigid Soviet conformity, surviving on theft and black market dealing when not in prison.

When the Soviet Union fell, the Vory emerged from the broken country’s peripheries to exploit the legal chaos. By all accounts, they infiltrated the top political and economic strata, while taking command of a burgeoning mafia that spread murderously through the post-Soviet countries.

The Russian news media covered the raid on the yacht this month with apparent delight. The major channels showed scenes of commandos marching the handcuffed gangsters single file to waiting buses.

Most were later released for lack of evidence connecting them to a crime. The authorities did not explain why they had conducted the raid if they had no basis to bring charges against those detained.

Some speculated that a major crime boss, Tariel Oniani, had organized the meeting to discuss a conflict with a rival don, Aslan Usoyan, known as Grandpa Hassan. The rift, reports said, threatened to erupt into a full-scale war.

“There will be war and there will be blood,” said the operator of vorvzakone.ru, an Internet portal that monitors the activities of the Vory. He insisted on anonymity because of the sensitive nature of his work. He said Mr. Oniani was at the meeting and detained, but not Mr. Usoyan.

In an interview with the newspaper Vremya Novostei, “Grandpa Hassan” denied rumors of impending violence.

“We are peaceful people and don’t bother anybody,” he said. “We are for peace, in order to prevent lawlessness.”

In fact the Vory have been linked to numerous brutal murders in the post-Soviet period. Authorities have accused them of ordering contract killings and carrying out kidnappings and innumerable financial crimes.

To be inducted into the Vory’s society involves a life devoted to crime, and, traditionally, an adherence to a strict ethical code, said Aleksandr I. Gurov, an expert on Vory who headed the organized crime units of the Soviet Interior Ministry and the K.G.B. He is now chairman of the commission on ethics in the Russian Parliament.

Compared with the Mafia in Italy, Mr. Gurov said, the Vory “have less rules but more severe rules.”

Vory must have no ties to the government, he said, meaning they cannot serve in the army or cooperate with officials while in prison. They must have served several jail sentences before they can qualify. They should not marry.

Ethnicity has rarely determined whether someone can join the club. Today, Mr. Gurov said, most Vory, even those active inside Russia, are from other post-Soviet countries and are not ethnic Russians. Then there are the tattoos. Just as a Russian Orthodox icon depicts the pious works of saints, the elaborate tattoos that the Vory wear detail their criminal exploits. They also indicate rank and occupation.

In modern Russia the Vory have a certain allure, in part because of their association with prison life.

“Very many people have passed through prison, even those who have had no special connection to the criminal world,” Mr. Konstantinov, the journalist, said. “This is a theme that has been very relevant for many families.”

This intimacy with imprisonment has spawned a pop culture particular to Russia, in which the Vory and other criminal elements have taken center stage. They recently went Hollywood, vividly portrayed in the film “Eastern Promises,” which won the top award at the Toronto International Film Festival last year. Mr. Konstantinov said the film was the most accurate depiction that he had seen.

Still, despite all the celebrity, the Vory no longer seem to wield the power they once did.

According to criminologists, in the late 1980s and the 1990s, as capitalism seeped in, new criminal players entered the field. Mr. Gurov said that unlike most Vory, the top leaders of the newcomers were college-educated, and these new gangsters swarmed into the legal void left by the Soviet Union’s collapse to snatch up lucrative shards of the shattered empire.

At first this new criminal class worked in tandem with the Vory, who helped arbitrate the gang wars that bloodied the streets of Russia’s major cities during the 1990s. In the last decade the Vory have suffered a declining influence, analysts generally say, as competitors with stronger ties to big business and the government squeezed them from their traditional niches.

“Vory are still strong in gambling and retail trade, but their significance in Russian economy and society is rather low,” said Vadim Volkov, a professor at the European University at St. Petersburg, who has researched criminal societies in Russia and the former Soviet Union.

Estimates of their numbers in Russia vary. Rashid G. Nurgaliev, the Russian interior minister, said recently that just under 100 remain active on Russian territory today, though others dispute that count.