On the outskirts of Changsha in southern China stands a new tower. Its size is modest by Chinese standards.
At a mere 204m it's less than a third of the height of Shanghai's tallest. Its blocky glass and steel form may be unlikely to win any architectural beauty awards.
But what is startling is the speed at which it was built. A time-lapse video shows it shoot up at the rate of three storeys per day.
For the man behind it, Zhang Yue, this is only the beginning.
“Humans have experienced revolutions in industry, agriculture, transportation and information, but not yet in buildings,” says the handbook of the company he founded, Broad Group.
Here now comes the revolution.”
The revolution will be modular, Zhang insists. Mini Sky City was assembled from thousands of factory-made steel modules, slotted together like Meccano.
It's a method he says is not only fast, but also safe and cheap.
Now he wants to drop the “Mini” and use the same technique to build the world’s tallest skyscraper, Sky City.
While the current record holder, the 828m-high Burj Khalifa in Dubai, took five years to “top out”, Zhang says his proposed 220-storey “vertical city” will take only seven months - four for the foundations, and three for the tower itself.
And it will be 10m taller.
But if that was not enough, Zhang Yue wants nothing less than to reimagine the whole urban environment.
He has a vision of a future where his company makes a third of the world's buildings – all modular, all steel, and all green.
“The biggest problem we face in the world right now isn't terrorism or world war. It's climate change,” he says.
Our buildings are holistically solving society's problems.”
Since the roof went on Mini Sky City on 17 February 2015, Zhang Yue's tower has attracted plenty of attention.
A YouTube video about the building has been watched three million times.
Newspapers in many countries have listed its eye-catching vital statistics: 19 atriums, office space for 4,000 people and 800 apartments, and of course the 19 days it took to build.
This last figure requires a slight caveat - the tower was built in two bursts: the first 20 storeys went up in a week in 2014, but red tape held up construction for a year, with the final 37 storeys completed in 12 working days in February.
For some, the speed of construction has raised a question. Can something built so fast really be safe?
In fact, Zhang says safety is the very reason he got into construction, seven years ago.
In May 2008, China was already gearing up for the big party that was to be the Beijing Olympics, when disaster struck.
A powerful earthquake hit Sichuan province, killing 90,000 and leaving almost five million homeless.
It was a national tragedy. Many Chinese people were appalled at how easily thousands of buildings collapsed.
The death toll among children particularly - killed during lessons as schools caved in on top of them - gave rise to much soul-searching.
“At that time, everyone was debating how to make safer buildings,” Zhang says.
He had already made a fortune from air conditioning - he had private planes, a fleet of luxury cars, expensive homes - and this gave him a motive to branch out.
Zhang travelled to Germany, Japan and the US to meet expert engineers, and all of them talked about steel. Steel structures were strongest, but also flexible enough to bend, not break, during a tremor.
The problem was cost - steel was prohibitively expensive for normal buildings.
So Zhang Yue's idea was to make a new, cheaper form of steel structure.
He set up a new wing of his company, called Broad Sustainable Building (BSB), and set to work with a team of architects and engineers.
In 2010 they made their first public prototype - a six-storey building built in a single day for the Shanghai Expo. Since then they've completed more than 30 buildings, including a 15-storey hotel in six days, a 30-storey hotel in 15 days, and the recent Mini Sky City.
The process is always the same.
Steel is delivered to one of Broad Group's six huge hangar-like factories, where it is machine-cut and welded into one of a few basic modules - a column, crossbeam or floor section.
These are then loaded on to lorries and driven to the site, where they are slotted into place like Tetris pieces, and finally bolted and welded together.
All modules bear serial numbers. The more advanced ones, like the 12m x 2m rectangular floor sections, come pre-installed with plumbing, electric wiring and air ducts.
The company says 90% of their buildings' components are prefabricated like this, with only interior finishing required on site.
A “configuration guide” on the company’s website allows prospective clients to select the type of building they require, from hotel to kindergarten to museum.
They can also choose extras, such as a “sky garden”, an “indoor farm” or a helipad.
To demonstrate resilience of the buildings, footage has been released of a model skyscraper surviving the equivalent of a magnitude nine earthquake.
In heavily polluted China, one of the most appealing features of the design may be the interior air quality.
High levels of tiny atmospheric particles called PM2.5 pose a serious health hazard in many cities - at one 20th the diameter of a human hair, they're small enough to lodge in the lungs and enter the bloodstream. Broad Group claims their technology stops 99% of them from getting inside their buildings.
The windows are designed not to open, partly for this reason. They're also made of quadruple-paned glass, one of the features which Zhang says makes his buildings “five times more energy efficient” than conventional ones.
Others are 20cm-thick wall insulation, exterior window shading and Broad Group’s air conditioning system, sold in dozens of countries around the world.
In a building like the proposed 220-storey Sky City, with 30,000 residents, there would be further benefits, Zhang argues.
People would live and work in the same building, so they would not need cars. By living vertically, more land could be left in its natural state.
“In Sky City, you can find anything you need from cradle to grave except a crematorium,” Zhang has written.
But how are his towers perceived in China?
Their simple, unadorned form may come as a relief to President Xi Jinping. He recently expressed exasperation at China's rush of avant-garde buildings that look like anything from ancient gold coins, massive teapots to huge pairs of trousers.
But whether Chinese consumers would want to live in an urban environment where many apartment blocks looked strikingly similar is another matter.
There have been other criticisms too. An engineering professor from Beijing’s Tsinghua University, Zhang Jun, has been widely quoted in the Chinese media arguing that modular buildings have an Achilles heel - a tendency for water to seep in between the modules over time.
He argues that reinforced concrete will continue to be the future of residential buildings, as anything under 30 storeys would cost too much - though he accepts that the Broad Group towers are structurally safe.
On a traditional bricks-and-mortar building site a stone's throw from Mini Sky City, civil engineer Chen Zhipeng identifies a different snag.
“I've been an engineer for 20 years, and I worry that if you run into problems while assembling a modular tower you can't fix them. That's the problem with pre-fabricated parts.”
But Zhang Yue scoffs at such talk. “That's a stupid way of thinking,” he says.
When you're building modular towers, you have to make sure every single detail is right before you begin.
“You can't be like a housewife making dinner thinking: 'Oh let's add some soy sauce, maybe a touch more vinegar.' No. You have to be a like a chef in a restaurant. You have to make exactly the same meal every time.”
Changsha is known in China as a cradle of revolutionary Communist leaders, and as a hotspot for fiery cuisine.
It's where Mao began his political career, and you find his favourite dish at every corner - red-braised pork belly.
It's not a place you'd necessarily expect to find a replica of Buckingham Palace, with a bronze statue of Napoleon on horseback in front of it, sword raised in a heroic charge.
Nor, for that matter, would you expect a 40m-high gold Egyptian pyramid.
But here they all stand at the centre of Broad Town, Zhang Yue's company headquarters.
Spread out over a square kilometre, it's home to 1,200 of the firm's 4,500 staff. Workers in blue overalls stroll from dormitory to factory across immaculate lawns.
A clucking of geese from the company's extensive organic farm punctuates the hum of giant air conditioning units.
Behind all of this is the man himself: Chairman Zhang Yue.
He's a visionary and uncompromising leader who has been described as a Chinese Steve Jobs - and Broad Town is his idea of a perfect society in miniature.
The “palace” is actually called the Environmental Philosophy Institute. All employees have to memorise a handbook called Life Attitudes of an Earth Citizen.
It contains Zhang Yue's detailed instructions for living a virtuous, healthy and environmentally friendly life.
“Don't buy things you only use once, such as newspapers.”
“Grow your own vegetables.”
“Most importantly, have only one child, to allow the population of the world to return to a level it can bear.”
Another company handbook urges staff to brush their teeth twice a day, and to share cars.
All job applicants have to memorise these rules during an arduous recruitment process, which includes a week's military-style boot camp.
The man himself is small and wiry, with a glimmer in his eye and an incredibly quick mind. He often works 14 hours a day, and eats just a single meal at 7pm, meaning he's usually grouchy by late afternoon.
His hair is greying. Dyeing your hair is bad for the environment, he says.
I have to set an example. My staff imitate me, and they then influence those around them. That's how we influence society.”
Zhang's office is dimly-lit to protect his sensitive eyes. There's no computer, just piles of papers, diagrams and charts scrawled all over in red ink.
A magnifying glass for scrutinising documents and architectural plans is the most prominent piece of equipment.
An endless stream of assistants waits by his office door for him to approve a poster, a budget, a meeting. He oversees every aspect of the business.
“It's all about the details. Engineering serves the people. You ask yourself: ‘What does society need? How can we make products which interfere as little as possible with the environment?’ This needs an unlimited amount of work.”
Zhang started Broad Group with his brother in 1988 and rapidly made it one of China's most profitable private firms.
By the early 2000s he was a regular in Forbes magazine's China Rich List, and now has an estimated fortune of $900m.
Broad Group's chief products are industrial-scale air chillers, air purifiers and air conditioning units. Their “non-electrical air conditioning” machines use natural gas, solar power and waste heat for energy.
Glossy company literature full of complex engineering diagrams and detailed technical specifications is available throughout Broad Town.
A control centre here with banks of flashing screens monitors air conditioning machines in more than 80 different countries, as engineers keep track of faults in Madrid, in Bangkok, or in Bracknell.
Flushed with the early success of his company, Zhang Yue developed a passion for flying, becoming the first Chinese citizen to buy a private plane.
At his peak he reportedly owned seven aircraft, but then sold most of them off. Private planes sit at odds with his more recent role as an eco-warrior.
“I love playing in my helicopter and can even fly it. It’s fun, but uses so much fuel. So I have to tell people: ‘Wealth comes with responsibility.’ And for those of us with environmental consciousness, wealth has no real meaning.”
He lifts a piece of paper. “I always write on both sides, look.”
He was given a United Nations Environment Programme Champions of the Earth award in 2011. Fortune Magazine called him one of the “world's top 25 eco-innovators” in 2014. He frequently attends international conferences on climate change.
“Chairman Zhang is the soul of the company,” says Broad Group vice-president Juliet Jiang, who has been with the company for 20 years.
“He majored in fine art. And later he taught himself thermal engineering, so he became the chief engineer for air quality products. Now he’s the chief architect for Broad Sustainable Building.
“He's not like the other bosses drinking tea, reading the newspaper, enjoying life, playing golf. No, Chairman Zhang spends his time all for his work.”
Company chef Deng Zhenyi, who was personally interviewed for the role by Zhang Yue 19 years ago, says his boss is a generous but also intimidating figure.
“He's strict with very high standards. Sometimes I feel a bit scared when I see him and hide,” he says.
The works canteen is quite unusual, he explains.
“All the ingredients are grown on our own organic farms: wheat, oil, flour. They're not from outside.
“If employees can't finish their food, they're punished with fines of 200 RMB ($30 / £20), and they're banned from eating here for two days.
“We are quite strict about waste. ‘Eat as much as you like, but don’t waste a drop.’ This is our company's culture.”
Community spirit is encouraged. All company employees gather in Broad Town's main square at 07:45 on Monday mornings to sing the company anthem.
Naturally, it's written by Chairman Zhang.
I love my company. Long may it flourish.
I love my clients. I wish them prosperity.
I love China. Let it be civilised and strong.
I love the Earth, I love the Earth. May it be healthy and beautiful.
After work, staff attend free art classes, play basketball or visit the gym.
“People have to enjoy living here,” says Zhang. “Otherwise it's an inhumane environment. With no productivity.”
Devotion to productivity also prompted another rule: no romantic relationships on campus.
Zhang Yue's background as an artist may explain the abundance of sculpture.
A bronze Plato and Aristotle remonstrate in front of the Environmental Philosophy Institute, a stylised Shakespeare lurks by the restaurant and revered poet Li Bai holds a cup of wine extravagantly aloft by the company hotel.
A Broad Group booklet called Immortal Wisdom contains quotations and potted histories of these great thinkers - Leonardo da Vinci’s “Simplicity is the ultimate sophistication” alongside the words of the late American management consultant Peter Drucker: “Innovate or die.”
By the company shop stands one of only three women immortalised in a statue on the campus: American environmentalist Rachel Carson, author of the influential 1962 polemic against pesticides, Silent Spring.
“She changed a lot of misperceptions. She inspired us to think about environment a lot earlier than others,” says Zhang, who sees himself as carrying her flame, and synthesising it with Chinese ancient thought.
“Lots of physical illnesses we suffer from today are caused by the environment. Spiritual stress and illnesses are a result of our blind materialism,” he says.
“In ancient Chinese medicine and philosophy, whether it's Daoism, Confucianism, medicine… we see things all as one process. You need to seek the source in everything. You need a holistic approach to solving problems.
“And in fact, Broad Group is doing that. We're solving the damage caused by the whole architecture industry on society and on the future.”
“If we don't build Sky City, all our towers are just dwarves. It has to be the tallest building in the world.”
In July 2013, on a patch of land an hour from Changsha's city centre, Broad Group managers stood shoulder to shoulder with local officials as earth was ceremonially shovelled around a foundation stone, bedecked in red ribbons.
China's media eagerly reported imminent construction of the world's tallest tower.
But it wasn't to be. A few days after the opening ceremony, work stopped.
In China buildings need a lot of paperwork, and some pieces were missing. The media quickly changed its tune.
Some commentators said Sky City was an ambition-driven, Babel-like, pie-in-the-sky vanity project.
Others that it was impossible to build so fast and that it was unsafe. Many simply wrote it off as a publicity stunt.
It was a bruising blow to Zhang Yue's pride, prompting him to release a highly personal three-page defence (including an instruction to newspaper editors that they could only publish it in its entirety).
In the following months, Broad Group laid low and pressed on with other projects, such as Mini Sky City.
But this tower too ran into problems with officialdom. The original proposal for a 97-storey building faced objections from Changsha’s airport authority, which pointed out it lay on a flight path.
This explains the one-year pause in construction, during which 40 storeys were lopped off the design.
A year after the original Sky City ceremony, in July 2014, some Chinese newspaper reporters visited the site again. They found a still empty field, but now overgrown.
One journalist revelled in discovering an industrious local farmer who had used a small patch of it to surreptitiously grow watermelons.
But if he thought he was bringing Broad Group down to earth, the company just says it is ahead of its time.
“The country's legal system and standards are still catching up with us,” says factory manager Xiao Changgeng.
“I'm sure the government will soon start supporting us with new policies and standards.”
Zhang says Sky City is about “washing away… prejudices - like formatting a hard drive”.
“They'll realise this building has everything you need in it.
“They'll notice it’s saved a lot on road construction, land construction, and that people who live here have a lot of time for leisure instead of bouncing around on the road all day. Their quality of life will be higher. They’ll be happier. Things like this.
“It has huge benefits for future generations. If you tear it down 500 years from now it will leave a steel skeleton which is a resource for them, not just a load of rubbish.
“That’s what this is about.”
To those who say that a few green skyscrapers will not halt climate change, Zhang predicts that once he has succeeded in bringing costs down, his company’s model will be “unstoppable”.
And as buildings use more energy than transport or industry, he says, the impact will be huge.
Zhang's driving personality may be the key to Sky City's future, says Dr Dario Trabucco, an expert on sustainable tall buildings with the Council on Tall Buildings and Urban Habitat, who has visited Broad Group's factories.
A key element in super-tall buildings is “the ego of the developer who wants to make a mark in history,” he says.
The Rockefeller, Chrysler and Trump buildings were all backed by a single-minded, wealthy individual.
In February, Zhang predicted that all the necessary permissions for Sky City would be obtained within three or four months, and that construction would start in late 2015 or early 2016.
And in the past few days, Hunan province - in which Changsha is located - has signalled further support for the construction of modular buildings.
“But in accordance with the regulations, buildings of 350m need to be approved at the national level in Beijing,” said a Broad Group spokesperson. “Because of this, the official start date for Sky City is still unclear.”
In the company’s Immortal Wisdom booklet, Napoleon's entry features the quote: “Difficult is a word only in the dictionary of fools.”
And as he addresses a conference hall full of Broad Group management at the company AGM, Zhang Yue - rumoured in Broad Town to be the same height as the French general - invokes Napoleon’s spirit.
“Napoleon conquered the world with the sword, but he said the greatest conquest is that of the heart. Only Sky City can conquer the hearts and minds of this turbulent era.
“You just have to build it tallest. One metre less won't do. It has to be the tallest building in the world, even one metre taller than the one in Dubai.
“With Sky City, we face even more problems than we imagined. Lots of people went against us, criticised us, but I won't be shaken. And even if there was 10 times as much criticism we wouldn’t budge.
“I have my reputation to think of - we’ll build it.
“And in a couple of years we're going to be booming.”