When I told Beijingers what my itinerary for their city included, they nodded along. The Forbidden City, of course. Tiananmen Square, yes. The Great Wall, naturally.

And then, when I listed my final stop – one almost as monumental as the Great Wall, as connected to the emperors as the Forbidden City and even more consequential to Beijing’s history than Tiananmen Square – they paused.

“The Grand Canal?” they asked. “Are you sure?”

If few Beijingers make it out to the Grand Canal, even fewer travellers do. The canal is a relatively well-known attraction in southern China, where barges and cruise ships alike ply the 2,500-year-old route. In Beijing, less so: hardly anyone realises that the canal runs an entire 1,794km north from Hangzhou to Beijing’s suburb of Tongzhou, located 35km west of Tiananmen Square.

Yet few spots are more important to Chinese history than this: the longest, oldest manmade waterway in the world, nine times longer than the Suez Canal. Without the canal, Beijing never would have been China’s capital. And without the canal, China may not be China at all – all reasons why, in June 2014, Unesco finally inscribed the Grand Canal on its World Heritage List.

I didn’t care if locals were perplexed. I had to see it.

As we drove west along highway 103, four lanes of traffic running in each direction, one building under construction loomed after another. People on scooters checked their iPhones at a stoplight; a concrete mixer churned behind them. As we crossed a bridge, I caught a quick glimpse of water beneath us. And then it vanished.

Whether the canal goes largely ignored by locals today or not, the workers who build here are continuing a millennia-old tradition: one of investing human capital in projects on the kind of scale the world has never before seen. Work began on the canal in 486 BC, but it wasn’t until a 7th-century expansion that the canal was brought to the magnitude it’s known for today: in 605, a 1,000km canal was cut from Luoyang to Qingjiang (now called Huaiyin), and three years later, 1,000km were built on to today’s Beijing. In 610, another 400km was cut from Zhenjiang to Hangzhou.

The project took more than three million peasants to complete. Half are estimated to have died from the hard labour and hunger. The canal’s further facelifts, including a major intervention in the 13th Century, took even more manpower. When Kublai Khan moved the empire’s capital to Beijing in 1271, eliminating the need for a section to go to the previous capitals of Kaifeng or Luoyang, he ordered that the canal be made more direct – creating today’s 1,794km Beijing to Hangzhou route. The project took four million slaves some 10 years. According to Unesco, in fact, the canal was “the world’s largest and most extensive civil engineering project prior to the Industrial Revolution”.

Like any major route, the canal played several roles, all of them indispensable to the empire. Food security was one: the Yangzi River Delta was China’s breadbasket, but the Yangzi itself flowed from west to east. As any ruler knew, hungry locals were more likely to rebel, and unfed soldiers couldn’t be counted on to keep both the peasants and potential invaders in check. And so (before Kublai Khan’s overhaul), the Grand Canal allowed barges to transport rice from the Yangzi to the Yellow River and on to Luoyang and Kaifeng, with an adjoining tributary allowing transport even further west to Xi’an, another of the ancient capitals. Meanwhile, wheat, which was grown in the north, could be sent south. By 735, no less than 149,000,000kg of grain was being shipped along the canal each year. Other goods, from cotton to porcelain, were also traded, helping China’s economy bloom. And the canal became a lifeline for communication, with government couriers running messages up and down the waterway.

A feat of modernity in itself, the canal led to equally extraordinary innovations. In 587, the world’s first lock gates were invented by the Sui Dynasty engineer Liang Rui for one of the canal’s original sections along the Yellow River; in 984, a transport commissioner named Qiao Weiyo invented the Grand Canal’s first pound lock – the lock that we see in modern canals even today, creating a pool with two barriers and allowing a boat to wait safely until the water level changes. (It wouldn’t be picked up in Europe until 1373, in Vreeswijk, Netherlands). 

Yet after railroads took over China in the late 19th Century, the canal was largely forgotten. Vast sections fell into disrepair. In 1958, the canal was restored. Today, some sections – particularly in the south – are plied by barges, mostly transporting construction material, while others remain unused. Here in Tongzhou, the section hadn’t been used for trade in years.

But the city seems to be rediscovering the canal’s merit. For the 2008 Games, an Olympic park was built along its shores; I could see the park’s white canopy rising from the fog like a Japanese crane.

And last year, the city built a new park: the Grand Canal Forest Park, which runs 8.6km on the north side of the canal in Tongzhou. On a Sunday morning, families pushed strollers and carried picnics beneath the park’s tree-lined walkways. Immaculate clusters of flowers and foliage grew, many with descriptive signs in both Mandarin and English. From a small amusement park, a carousel tinkled a tune. 

Smelling the brine on the air, I wandered past the families, past the rides. And there it was.

The Grand Canal was wider than I’d expected, and stiller too.  Lotus flowers blossomed at the edges of the grey-green water. I couldn’t see a single skyscraper on the horizon. The only movement was a tiny boat, no more than a creaky platform with a sputtering outboard engine; its crew of three old men looked like they were trawling for fish. Floating in and out of the mist that hung thick in the air, they seemed like apparitions.

At the dock, wooden boats lined up to take curious customers across. As mine puttered down the canal, another boat passed, this one without so much as an engine, just an operator rowing wooden oars. A handful of locals were on board for a Sunday outing. We waved at each other, and they smiled curiously: what was a tourist doing all the way out here?

Once, the canal had been proof that China was on the fast track. And I’d been drawn by its monumentality, its grandeur, its importance. Yet today, as Beijing builds bullet trains and underground metros, expands its airports and thrusts skyscrapers into the sky, the Grand Canal is anything but. It seems, instead, a symbol of a slower-moving past. And, if I could have, that’s what I would have explained to the perplexed passersby on the canal: in the end, my choice to come here was worth it not because the canal was as monumental as I’d expected – but because, on the scale of modern-day Beijing, it was less so. And that made it a refreshing stop.

The Beijingers I’d spoken to may have been right; today’s vast, almost empty waterway makes it hard to get a sense of just how extraordinary the Grand Canal once was, and how integral it was to China’s flourishing trade. But as Beijing races ahead, building modern monuments to commerce, industry and traffic, experiencing the canal – stepping outside of the rush, experiencing a place of lotus flowers and fishermen, faded pride and stillness – seems all the more poignant.