"Nothing is easy in Iran, but there is always a way." An Iranian businessman makes small talk in the arrivals queue at the Imam Khomeini Airport in Tehran. I nod with a knowing smirk. Numerous phone calls from London to the ministry of culture in Tehran eventually pushed through approval for my working visa application, albeit three days after I was supposed to fly out. Inconvenient, but I nevertheless feel slightly smug as I show my ten-day permit - a rare commodity these days - to the passport official.

A few days later I'm led to a backstreet of south Tehran, to a green door with stone steps that spiral downwards. As I descend, the drumming and wailing reverberate louder. This zurkhaneh, or "house of strength", where wrestlers meet for physical and spiritual training, is 300 years old. The traditions of the "sport of heroes", as it is called, go back more than two millennia to the Persian empire. Iran's martial art, I learn, means far more to Iranians than just a sport.

I am fortunate the zurkhaneh is open. Most are closed because it is a public holiday - the Heavenly Departure of Imam Khomeini, which remembers the former supreme leader's passing in 1989. Even Tehran's awful traffic - thanks to 15 million inhabitants and subsidised fuel prices at five pence a litre - has abated. Tehran means "end of the road", and the city does indeed finish where the Alborz Mountains to the north start. Beyond them is the Caspian Sea and plentiful oil and gas reserves. Today, a sallow smog obscures the remnants of snow on their peaks.

Wealthy Iranians live in marble high-rise blocks of flats in the fresher north, almost halfway up the mountainside. It's a ten-kilometre taxi ride to the humid streets of the more deprived south - smoky and noisy from the bustle of kebab sellers, revving mopeds and beeping horns. On the way, the taxi driver asks where I'm from. "Britain," I smile. He looks disappointed but then, with an ounce of irony, replies: "Anyway . . . welcome to Iran."

Below the streets, inside the zurkhaneh, is a domed ceiling, and underneath this is a hexagonal pit where 15 well-built men are exercising, gracefully rolling weighty wooden clubs over their shoulders back to their barrel chests. It is oppressively hot and sweaty. Above them on a podium is the morshed - their "guide" - who plays a drum and chants what sounds to foreign ears like a call to praye r. It feels more like a place of worship than a gymnasium.

Next, each man takes his turn to spin, arms outstretched, and at ferocious speed. My guide, Omid Khazani, tells me it's to prepare for diz ziness in battle. Omid is a government "interpreter" who goes everywhere I go. In his inside jacket pocket he holds a permission letter with a list of interviewees and locations I've specified. If I travel beyond a 15-mile radius of central Tehran, he says politely, he has to make a phone call. He is softly spoken and extremely hospitable, but there is inevitably a little tension in the air.

Omid is, however, well informed about Persian history and culture. He tells me the morshed chants salutations to Shia imams. At other points in the ceremony, the morshed recalls mythical characters and battles from ancient Persian literature. At another, he cries: "Iran will not give one inch to foreign powers!" It's no wonder the national team has dominated Olympic-style wrestling for decades: Iran's cultural heritage, its politics and its religion are bound up in the sport.

The walls of the zurkhaneh are covered with framed pictures. Images of Imam Ali, the holiest figure in Shia Islam, a fearsome warrior who used just one strike of his sword to slay his adversaries. Paintings of Rostam, the wandering hero from the Shahnameh, or "Book of Kings", a 10th-century text found on every Iranian's bookshelf. Also, sepia photographs of 19th-century wrestlers with impressive handlebar moustaches, reminiscent of circus strongmen.

What they have in common, Omid tells me, is that they are all Pahlavan, or heroic cham pions. They embody the masculine ideal of physical strength combined with javanmardi, or chivalry. These characters, whether mythical, religious or Olympic, are what the Iranian man is supposed to aspire to: tough yet humble - gentle giants, if you like.

One of the photos from the 1950s is of Gholamreza Takhti, an Olympic gold medallist whose name and image are omnipresent in Iran. Stadiums and streets are named after him; his picture hangs in restaurants and tea shops all over. To compare Takhti to a sports personality - say, Muhammad Ali in boxing - would belittle his importance to Iranians. The Dalai Lama or Mahatma Gandhi would be closer to the mark. Thousands go to his grave each year on his anniversary. A devout Muslim and an open critic of the shah, he was found dead in a Tehran hotel in 1968. Many still believe the Savak, the shah's secret police, murdered him. The official line is that he committed suicide.

Takhti supported the nationalists led by Muha mmed Mosaddeq. When Mosaddeq was democratically elected prime minister in 1951, his first move was to nationalise the oil industry and take power and profits from the British and the Americans. Within 16 months, Churchill and Eisenhower responded - a CIA-instigated coup d'état overthrew Mosaddeq and replaced him with Shah Reza Pahlavi, who enforced the rule of an almost police state to curb demonstrations.

In this context, Takhti stood for the "people" against the "Establishment". Before the revolution finally came in 1979, the Ayatollah Khomeini, though exiled in Iraq, and his supporters were quick to appropriate Takhti's name for the cause. The Takhti Cup, an international wrestling competition, recalls his life and also commemorates the Islamic Revolution.

The values Takhti stood for are still promoted today. The International Zurkhaneh Sports Federation (IZSF) was set up five years ago, under the auspices of Ayatollah Ali Khamenei, to combat crumbling ethical values in Iranian society. Its big plan is to nurture the Pahlavan both here and beyond Iran's borders to promote peace. Last year, the IZSF set up a zurkhaneh in Baghdad, and others have sprouted in Kabul, Beirut, Seoul and even New York. There could be one in London by next year.

I couldn't help but think that reaching back to Iran's golden age of chivalry through wrestling was symptomatic of the nation's struggle to cope with the modern world on its doorstep. Omid says the upholding of these values, through institutions such as mosques and zurkhaneh, with their determination that corrupt ideals will not colonise Iran, has often sparked uprisings. I have warmed to my guide and his peaceful demeanour. I have a home in his Tehran apartment any time I wish to return, he says. Omid is no more a wrestler than I, yet he has an almost Herculean belief in the right way to behave. Like many of the obliging and humble Iranians I met, he gives the sense that he would perhaps be prepared to pick up the sword to defend high morals, religious or otherwise.