Whenever talk turns to the city of Hangzhou and its splendid geographical attributes, you can be almost certain that topping the list will be West Lake with its beauty, tranquility and important place in literary and artistic history. Somewhere on the list, too, will be the scenic Xixi National Wetland Park with its sprawling ponds, lakes and swamps. Then glance a little further down the list beyond those water features, and another will roar into view: the mighty Qiantang River.

What the Qiantang lacks in idyllic traits compared with the other two landmarks is more than compensated for by the majesty of its power-a force that has put the brightest of Hangzhou minds to the test over the centuries as they have tried to tame it.

For all that, the Qiantang knows how to put on a show for tourists and others, too.

The river, stretching over more than 500 kilometers and flowing into the East China Sea, runs from Anhui province to Hangzhou Bay, along the way delivering a view of one of the most spectacular tidal phenomena anywhere in the world.

Every year around the Mid-Autumn Festival, when the tide is at its maximum force, visitors gather in the town of Yanguan, about 60 km northeast of Hangzhou, to take a glimpse of the power of nature.

The tide can climb to more than three meters from the rising water surface at a speed of 5 to 7 meters a second. It means an eight-meter dispersion from the normal water level when there's no tide.

So written history has it that on and off, over about a millennium, beginning during the Tang Dynasty (618-907), a wall stretching 300 km was built along the Qiantang River's estuary as a protection against the tidal threat.

This construction project was as significant as the Great Wall and the Grand Canal, says Lang Xufeng, director of the cultural heritage preservation center that is part of the municipal bureau of gardening and cultural relics of Hangzhou.

At one point in history the Great Wall was renowned for its role as a military defense and as the boundary line between farming and nomadic civilizations. The Grand Canal, running 1,800 km from northern to southern China, served as an important channel for transporting grains and reinforced the empire's control of the south. From Hangzhou it took in dynastic capital cities such as Beijing, Kaifeng and Luoyang in Henan province.

The seawall, mainly in southeastern coastal areas, has not been given as much attention as the Great Wall or the Grand Canal, nor the acclaim that it and its builders no doubt deserve.

Over 2,000 years the seawall has been built and destroyed, destroyed and rebuilt to prevent the tide from swallowing the fertile lands of Jiangsu and Zhejiang provinces and part of what is now Shanghai, a traditional economic center of the country.

The area, covering the lower reaches of the Yangtze River and the Taihu Lake regions, accounted for the major part of the agricultural feudal empire's tax revenue, especially between the Song (960-1279) and the Qing (1644-1911) dynasties, Lang says.

The section of the ancient seawall that remains along either side of the river today was built mainly of stone, wood or dirt. The tide hitting the northern bank of the Qiantang was particularly threatening, so extra attention was given to ensuring that the seawall on this side of the river would hold firm.

The seawall provided Hangzhou with a safe and stable natural environment as it kept salty sea water from flowing backward and hardening the soil.

In recent years ancient relics of the wall have been found mainly in urban districts of the city such as Shangcheng, Jianggan, Yuhang and Xiaoshan, some dating back to the time of the Five Dynasties and Ten Kingdoms (907-960).

Unfortunately, many relics lie buried as a result of reclamation and changes to the river channel and city construction, which in turn has resulted in public indifference to the seawall's existence and importance and even outright ignorance.

Some parts of the wall exposed above ground are said to have been handled incorrectly, putting its continued existence in danger. For example, a part of seawall located in what was formerly known as Rongxing village of Xiaoshan district, 20 km from downtown Hangzhou, was reported to have been covered by building refuse, a local media report in 2019 said.

When a cultural and sports center was being built in Jianggan district, 12 km from the city center, in 2013 a 300-meter seawall built during the reign of the Qing Dynasty emperor Qianlong (1736-96) was discovered.

It was built by stones, all of similar dimensions, about 1.5 meters long, 40 cm wide and 30.5 cm tall, joined by a kind of glue mixed from sticky rice juice and cypress vine.

The stones were piled up to 17 layers high, with those at the top bound by embedded iron bars.

The lower layers jut ever further into the river, with each higher layer receding toward the shoreline, making the seawall, when viewed from the side, resemble fish scales-giving the style of seawall construction the name yulin, meaning "fish scales" in Chinese.

In front of the stone wall was a stack of pinewood piles penetrating into the riverbed aimed at protecting the stone and withstanding the force of the tide. The piles remained almost intact in water for more than 200 years, oil protecting them from decay.

The site has been turned into the country's first seawall museum, opened a year ago, with a 30-meter section of the seawall on display and the evolution of seawall building techniques explained.

Yao Qian, director of the cultural heritage preservation center of Jianggan district, who also serves as a museum guide, says the road connecting Hangzhou and Shanghai built in the 1930s exactly covered the seawall because there was no need to lay the foundation again, which had a spin-off benefit of preserving ancient relics.

Three emperors of the early Qing Dynasty, Kangxi (1654-1722), Yongzheng (1678-1735) and Qianlong (1711-99) had attached great importance to maintaining the seawall.

Emperor Qianlong got a good view of the seawall on the Qiantang River on six trips he made to the lower reaches of the Yangtze River. On four of those trips he lodged in Haining, about 60 km east of Hangzhou, and closely inspected seawall construction there.

It cost about nine households' annual family spending at the time to build just one meter of such a seawall, and in Qianlong's reign nearly 47 kilometers of yulin-style seawall were built, Yao says.

Because of the cost, the project took years to complete, but over the decades people managed to turn the seawall in Haining that had to keep back the most turbulent tides into the sturdiest of yulin-style seawalls.

Over the 60 years of Qianlong's reign he spent 3.8 million liang of silver on the project. A liang was an ingot forged from gold or silver and used as a form of currency, a single unit of which in this instance equates to about 300 yuan ($45) today, meaning the emperor poured more than 1 billion yuan into it.

Nevertheless, Yao says it is an exaggeration, as popular lore has it, that Emperor Qianlong spent one-third of the empire's income on building the seawall, but the extent of the spending reflects the great importance people of the time attached to the project.

Another popular tale has it that during the late Eastern Han Dynasty (25-220) a local officer, Hua Xin, led citizens to build the earliest seawall using just dirt or firewood to resist the tide's impact on agriculture.

Today's celebrated West Lake was just a seasonal lagoon surrounded by a sandbank at the time, and how they looked at any time depended on the level of sea tide; the urban area was just a shallow bay.

The construction of the seawall severed the lagoon from the river and the sea.

The lagoon then gradually turned into the freshwater lake we know today, and the sediment brought by river current continuously changed the riverway and the land shape, according to the city planning exhibition hall of Hangzhou.

During the Five Dynasties and Ten Kingdoms, the king of the Wuyue Kingdom, Qian Liu (852-932), promoted the first major technical innovation in building the seawall as laborers put stones into long bamboo cages that were piled together to impede the tide.

In later centuries Zhejiangers developed efficient, advanced construction skills, improved management and investment, and worked to prevent corruption.

For example, during the Ming Dynasty (1368-1644) an officer named Huang Guangsheng (1506-86), the inventor of the yulin-style seawall, created a labeling system to facilitate maintenance of the project.

The seawall was divided into 140 sections, each about 70 meter long and marked with a Chinese character in an order according to the One Thousand Character Primer, a widely taught primer for children going back more than 1,400 years.

The system made it easier to recognize those who built a certain section. They would be responsible for repairing their own part of the wall and face penalties for any shortcomings.

The Qing Dynasty also set up an annual maintenance regime under which the construction workers would be responsible to maintain their work for 10 years.

During the process, local officers of Zhejiang, a province with a rich business ethos, used spare money for lending, and soon the province was able to cover the expense without fiscal support from Beijing.

And according to Lang the provincial-level administration's taking care of river harnessing, seawall building and flood defense of the Qiantang River stems from the administrative system of the early 20th century, and efforts to reinforce the seawall have continued to this day.

The provincial water resources department launched a project last year to strengthen the seawall of about 2,000 kilometers that extends along the province's estuaries and sea shore by 2030.

The project, aiming to improve the seawall's capability of resisting typhoon and storm surges, is to optimize a project completed at the end of the 20th century that has proven to be invaluable, but that was limited by financial constraints of the time.

Chinanews.com said in November that over the previous 20 years the number of people who benefit from the seawall's protection in the province had nearly doubled and GDP had risen about 15-fold.

The seawall around the Hangzhou Bay area alone has been protecting a population of more than 16 million.

The original construction standard has lagged behind economic and social development, Chinanews.com said, adding that the new project will also integrate ecological, cultural, landscape and recreational considerations.

Construction of 150 kilometers in the cities of Jiaxing and Taizhou was due to begin within the year, the provincial government said in July.

Governments and academics in Hangzhou and neighboring cities such as Haining are expecting the seawall, together with natural features and cultural legacies related to the Qiantang River, to be out on the UNESCO world heritage one day and are promoting research, archaeological discovery and preservation of ancient relics.

Hangzhou already has the West Lake Cultural Landscape, the Grand Canal and the archaeological ruins of Liangzhu city inscribed on the World Heritage list.

Having a long-term vision helps raise people's awareness that the city of Hangzhou owes its development to the Qiantang River, Lang says.

"In all, our ultimate goal is to protect the ancient seawall."

Influential Zhejiang businessmen including Jack Ma, the founder of Alibaba, Zong Qinghou, founder of the beverage maker Hangzhou Wahaha Group, and Lu Guanqiu, the late founder of the automotive parts company Wanxiang Group, have often been referred to as "tide players of the time".

The description was originally used to hail the bravery and ambition of those who would like to tame, or at least keep in check, the Qiantang River.

In Yao's eyes, seawall construction is also a reflection of such a spirit, and the willingness to be a "tide player of the time" is deeply rooted in the city and its citizens, she says.