For an answer one must look back in history. Descended from the Tartar horsemen who invaded the steppes of Russia with Genghis Khan, the Cossack Hosts have been consistently topped up over the centuries by runaway serfs, disaffected Old Believers and rascals who had fallen foul of central government or local landowners. Once they were accepted into the Cossack community, the rules of the Foreign Legion applied: fierce discipline but no questions asked about the past. Good horsemanship, keen markmanship and a vague adherence to Orthodox Christianity (Jews and Turks were not welcome) were the only recruiting requirements.
At first, the Cossacks were almost wholly predatory: they hijacked passing caravans and raided neighbouring settlements, carrying off women and weapons. But gradually these poachers turned gamekeepers. In the 16th century, Ivan the Terrible started recruiting them to police his frontiers. The Tsar and the Stroganov family sent them into Siberia to conquer new territories and enrich the treasury with bales of rare furs.
They were always awkward servants of the crown, jealous of their privileges and tax immunities. They rebelled repeatedly: Stenka Razin's revolt threatened Moscow; Mazeppa betrayed Peter the Great; Pugachev nearly unseated Catherine the Great. Each time there were reprisals.
The turning-point came with Napoleon's invasion of Russia in 1812. The Cossacks threw in their lot unequivocally with the Tsar and harassed the invader's retreating army across the snows so effectively that Napoleon described them as "a disgrace to the human species". The British, on the other hand, feted them in Hyde Park. In the following century the Tsars deployed the Cossacks as storm troopers in their campaigns to extend their frontiers in the Caucasus and Central Asia. They were Russia's Gurkhas.
With the first rumblings of the Russian Revolution in 1905, the Tsar switched their role from frontier troops to internal policemen. With their knouts and sabres they slashed their way through strikers and demonstrators. But, when the final crunch of the Revolution came in 1917, they fought on both sides. Lenin branded them as kulaks and starved them out.
Some Cossacks always yearned for an independent Cossack state, and, when Hitler made false promises of this during his invasion of 1941, many defected and fought with the Germans while others remained as Red Army cavalry. Retribution was savage. Those who were captured or handed over by the Allies were executed or sent to Siberia; Cossack communities were decimated, and Cossack horsemanship reduced to a circus act.
With the collapse of the Soviet Union, the Cossacks bounced back. They had been put down before and survived. Yeltsin had a soft spot for them, reintroduced Cossack regiments and appeared in Cossack uniform. Cossack clubs - mostly rifle clubs - sprang up. They have not lost their old animosity for the Muslim Chechens, nor their propensity to protect Russia's frontiers bravely while resenting central authority. Even if some of the urban "Asphalt Cossacks" lack the old equestrian skills, it would be an unwise president who wrote them off as an anachronism.
"We are Russians, only more so," one of them said to me recently: I wouldn't quarrel with that. In fact, I wouldn't quarrel with a Cossack at all.
Sir John Ure is the author of `The Cossacks' (Constable, pounds 20)