신비한사전

I saw in a documentary that it's still usable today. I wonder what would have happened if Rome hadn't fallen; their technology was incredible. 2,000 years ago, the Romans brought spring water from 86km away to the city without a single pump. The secret was a barely noticeable gradient, dropping only 1 meter for every kilometer. But things got complicated when a deep gorge appeared right in the middle of the path. Initially, they built a 50-meter high structure of stacked stone arches and placed the water channel on top. That's the famous Pont du Gard. The problem was a gorge over 100 meters deep. Building a bridge that high was simply impossible in terms of cost and time. So, the Romans flipped the concept: they confined the water in lead pipes, plunged it down to the bottom of the gorge, and then pushed it back up the opposite slope. If the destination tank was even slightly lower than the starting tank, the water would naturally find its own level and rise. The aqueducts of Lyon crossed a 120-meter deep gorge using this method with nine pipes.

Props to our Russian bros! 250 years ago, Russia declared they would move a stone weighing 300 elephants to the city. But half of this stone was buried in a swamp. When they tried to pull it, the ground would collapse and it would just get stuck. So they waited for the dead of winter when the ground would freeze solid. Even with 400 people pulling, it wouldn't budge due to friction. Finally, they flipped the idea. Instead of pulling, they decided to roll it. They laid out grooved rails, placed bronze spheres all over, and put the stone on top. It started to slide forward 150 meters a day. They pushed it for 6 kilometers, even built a special boat just for this stone, and it arrived in 2 years. Using this principle, 20 years before the ball bearing patent, humanity left the heaviest stone moved without machinery in the Guinness Book of Records.

Rocket fuel tanks are made by joining thin, paper-like sheets of special aluminum. But the moment you melt and join this aluminum, the strength in that spot plummets. Tiny, invisible bubbles and micro-cracks start to form inside. Engineers would pre-thicken the seams, X-ray them, dig them out, and re-weld them repeatedly. However, the added weight meant less cargo could be sent to space, and once melted, the joint never regained its original strength. Then, in 1991, British engineers flipped the script. If melting weakens it, why not just avoid melting it altogether? By pressing the seams firmly with a rotating tool, friction heat softens the metal. Then, it's mixed together like kneading clay. Since it was never melted, there are no bubbles, and the strength remains almost fully intact. Today, both Falcon 9 and NASA's super-heavy rocket bodies are joined using this method: 'Friction Stir Welding'.

I think I saw this in an architecture documentary. It took a year just to dry it out, which explains why it's lasted so long. This is a place called 'Yongding Tulou' in Fujian Province, China. It's an incredibly old, circular earthen building constructed around 1308. To prevent groundwater from constantly seeping up from the ground, our ancestors first built a sturdy foundation wall of gravel and stone, 1 meter high. Plus, they used a clever waterproofing technique, meticulously filling the gaps with a mixture of lime and sand clay. On top of that, they erected an earth wall a whopping 1.8 meters thick, with bamboo pieces densely layered every 30 centimeters in height. The bamboo essentially acted as the rebar used in modern buildings. Aren't our ancestors' wisdom truly astonishing? The real amazing secret of this building lies in 'weight distribution'. It was designed so that the outer circular earthen wall bears the entire load of the building. Thanks to this, even though the ground subsided over time and the internal wooden pillars tilted a staggering 15 degrees, it didn't collapse and has stood strong for 700 years.

In the Joseon Dynasty, with no cranes or trucks, a massive project to build a fortress over 5.7km long began. Everyone thought it would take at least 10 years. Jeong Yak-yong used a 'Geo-jung-gi,' a device with eight pulleys, to effortlessly lift heavy stones. By standardizing stone sizes and mobilizing specialized equipment like the 'Yu-hyeong-geo' and 'Nok-ro,' the construction was completed in just 2 years and 9 months. Furthermore, all processes were meticulously recorded in the 'Uigwe,' enabling future restoration...

Hanyang was a basin surrounded by mountains on all sides, and the firewood for hundreds of thousands of people came entirely from those mountains. The bare mountains, stripped of trees, would pour out soil and sand whenever it rained, and that soil would fill the streams, causing floods. Digging it out was endless. Joseon's answer was to lock down the four mountains surrounding the capital entirely. They designated them as forbidden mountains, banned logging, erected boundary markers, and assigned forest rangers. The official reason stated in documents was timber for building the palace, but while that law was upheld, the tree roots held the soil of the mountain behind Gyeongbok Palace...

300 years ago in Joseon, there was no electricity or refrigerators. Ice cut from the river in winter would melt away with just a spring breeze. So, craftsmen dug into the ground and buried half of a warehouse. They covered the roof with soil and even planted grass. However, the hot air that seeped in when opening and closing the doors got trapped inside, continuously melting the ice. Finally, they flipped the concept. Instead of blocking the hot air, they made it exit on its own. They gathered hot air in recessed pockets between the arched ceiling and let it out through ventilation, and the melted water flowed out through the sloped floor. Finally, by tightly wrapping the ice with rice husks and straw, the winter ice survived until mid-summer. This is how Joseon's natural refrigerator, the Seokbinggo, was born...

Walking around Seokchon Lake to see the cherry blossoms, did you know it was actually a remnant of a river left behind by people who dammed the Han River in 1971? Jamsil was originally an island with mulberry fields, and the current Jamsil land was formed by blocking the southern Songpa River with soil. The problem is that the remaining water was trapped in a place up to 5.1m higher than the adjacent Han River, and on a sandy bottom where water drains easily. That's why they're still pumping up Han River water to pour into it, with 2,000 tons leaking out daily. In 2011, when Lotte World Tower was being built, the lake's water level noticeably dropped, prompting an investigation by the Seoul Metropolitan Government. Beneath your feet is the old riverbed filled with coal briquette ash, and before your eyes is water drawn from the Han River, even today...

Roads that were fine suddenly develop holes the size of a pot overnight. In Korea alone, over 500,000 are created and filled each year. Why do roads that can withstand trucks weighing tens of tons suddenly break apart after it rains? The culprit is water. When water seeps into the asphalt cracks and freezes on a winter night, it pushes the road apart from the inside. That's why nowadays, instead of blocking water, they use permeable pavement that allows it to pass through and drain. Apparently, less water splashes up on rainy days for the same reason...

Mixing glutinous rice soup into lime mortar causes the starch to bind crystal growth, resulting in a dense hardening. The walls built with this mortar survived a magnitude 7.5 earthquake in 1604. Even today, this glutinous rice mortar is used to restore old walls instead of cement. The power of rice was real.