At the farthest end of the Great Wall, Yang Yongfu limps along the section he arduously restored, in effect "privatising" it and putting himself on a collision course with the authorities.

The farmer spent five million yuan ($800,000) and years of backbreaking work renovating several hundred metres of the national symbol deep in northwestern China, turning it into a tourist site.

"At the beginning people didn't understand why I took on this project. They called me crazy," said the 52-year-old.

The Great Wall is not a single unbroken structure -- nor is it visible from space -- but stretches for thousands of kilometres, from Shanhaiguan on the east coast to Jiayuguan in the windswept sands on the edge of the Gobi desert.

In places it is so dilapidated that estimates of its total length vary from 9,000 to 21,000 kilometres (5,600 to 13,000 miles), depending on whether missing sectors are included.

First begun in the third century BC, parts were still being built in the Ming Dynasty (1368-1644), among them Yang's section.

It was little more than a ruin when he started work in 2000, but now 790 metres of ochre wall run out from a small fort across a stony plain, snaking upwards over a bare hillside via several watchtowers.

Built of bricks and rendered with earth, his wall averages around 4.5 metres high and is topped with battlements.

"People were sceptical, because they thought renovating the wall was the job of the government," said Yang. "I was surprised at the success I had. But this could also be considered an act of patriotism."

He set up an entrance area for tourists, complete with a car park and fishpond, and his wife Tao Huiping collects the 25 yuan admittance fee at the ticket booth -- a table in the open air.

"Today about 30 people came," she said, holding up the ticket stubs, beaming proudly and praising her husband's "phenomenal" work. "People call him Emperor Yang," she said laughing.

Their opportunity came about in 1999, Yang said, when local authorities called on residents to renovate the Wall themselves, and officials gave him authorisation to do so. The money came from savings and loans from relatives.

In recent decades the Wall has suffered the depredations of farmers stealing its stones for building, and construction crews cutting through it with roads and railways.

Some of the greatest damage came during the turmoil of the 1966-76 Cultural Revolution.

But as China has become wealthier the government can better afford to take on the burden of restoration.

At the same time the Communist Party uses nationalism to bolster its claim to a right to rule, and in recent years authorities have become keener custodians of symbols of China, from historic monuments to giant pandas.

A 2006 law gave the government the exclusive right to manage national relics -- making Yang's project illegal.

His business continues to operate but he and the local authorities have been through several rounds of negotiations over transferring the rights to the wall. They have so far failed to reach an agreement.

"I never received any support from the government and they accused me of constructing a fake wall. That's what makes me angry," Yang said.

One of the Wall's most popular sections, at Badaling just north of Beijing, can see tens of thousands of Chinese tourists during public holidays.

But even with 20,000 visitors a year Yang's site is a long way from being a viable business -- and just across the valley an official attraction listed as a World Heritage Site offers 7.5 kilometres of wall.

Yang admits still owing one million yuan. "I have cried tears of despair," he said, but insisted he "regretted nothing".

Jiayuguan city's head of cultural heritage Ye Yong explained that Yang's work was approved in a particular context. "It was a unique time in which the government did not have enough money to renovate or protect its heritage," he said.

"But going forward, with the new laws and regulations about the protection of cultural relics in place, individuals will no longer be able to do renovations themselves."

Even so, the farmer could yet reap a windfall from his investment if the government decides to "renationalise" it by including it in an official preservation project, Ye signalled.

"We will consider buying it," he said.