15 Most Astonishing Feats of Human Engineering
15 Most Astonishing Feats of Human Engineering
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00:00It's time to travel the world to see the top 15 most astonishing feats of human engineering.
00:05Let's start with number 15, the Millau Viaduct in France.
00:09This viaduct is a cable-stayed bridge that crosses the Tarn River Valley near Millau in southern France.
00:15It was designed by the French structural engineer Michel Verlagaux and the British architect Norman Foster,
00:20with the aim of reducing traffic in the nearby town and to provide a direct route for the A75 motorway.
00:26The final design was made up of 11 slender piers, the tallest of which rises to over 1,100 feet or 343 meters,
00:34making it the tallest bridge in the world.
00:36Construction began in October 2001 with each pier built on-site using climbing formwork,
00:42which is a technique that allows for continuous pouring of concrete.
00:45This ensured the strength and stability of the piers as they reached their full height.
00:49Once the piers were completed, the deck was added, which has been prefabricated in sections off-site.
00:55Each of the sections weighing up to 2,300 tons were transported to the site and lifted into place using a complex system of cranes and
01:02temporary supports. The deck, made of steel and concrete, was incrementally installed from either end of the viaduct,
01:08which, while being more efficient, required meticulous coordination and control to make sure they'd fit.
01:13The final stage was the installation of the cable-stayed system.
01:17Each of the seven masts rising above the deck supports a series of cables that fan out to hold it in place.
01:23These cables were carefully tensioned to create the desired curvature and load distribution,
01:28ensuring both the stability and beauty of the bridge.
01:32Number 14. The Grand Canyon Skywalk, Arizona.
01:36A number of glass bridges have been built in sites of scenic interest around the world,
01:41but the one that's the most impressive in terms of both its design and its location is the Grand Canyon Skywalk in Arizona.
01:48Extending out over the edge of the world-famous Grand Canyon,
01:51it offers visitors an incredible view of one of the world's most important natural wonders.
01:56The glass bridge is horseshoe-shaped and reaches a distance of 70 feet or 21 meters out from the canyon's rim,
02:03allowing you to look over 4,000 feet down to the Colorado River below.
02:07Done in collaboration between a businessman from Las Vegas and the Hualapai tribe that gave permission to use the land,
02:14it first opened to the public in 2007.
02:16At first, the foundations were installed, which are a series of high-strength steel piles that were driven 46 feet into the bedrock,
02:22ensuring the structure would be anchored securely.
02:26The main structure is then made of steel and glass.
02:28Now, the steel frame was fabricated off-site and designed to handle the loads created by both the environment and the visitors.
02:35This frame was transported in sections to the site and assembled on the edge of the canyon,
02:40and cranes and specialized equipment were then used to maneuver the heavy sections into place.
02:45The walkway's deck is made up of five layers of laminated glass specially manufactured to provide both strength and transparency.
02:52Each glass panel weighs approximately 1,200 pounds or over 540 kilograms.
02:58They were transported to the site and carefully installed.
03:01Testing was conducted throughout the construction process to ensure its stability, and the skywalk was, in the end, built to hold up to
03:0871 million pounds or 32 million kilograms, far more than the expected maximum load of visitors.
03:15Amazingly, it was all finished within just four years, and it's now become one of the most popular attractions in the region,
03:21giving a view of the canyon unlike anything else.
03:25Number 13. The Taj Mahal in India
03:29The Taj Mahal in Agra, India is one of the most recognizable and visually impressive structures on the planet.
03:36Commissioned by Emperor Shah Jahan in 1632 as a memorial for his wife, Mumtaz Mahal,
03:42it's now a UNESCO World Heritage Site and one of the most iconic symbols of India.
03:47Beginning with the selection of a site along the Yamuna River, which allowed for the easy transportation of materials,
03:52a 10,700-square-foot or 1,000-square-meter platform of compacted earth and stone was created
03:59to support the structure and ensure its stability on the soft riverside soil.
04:03One of the most notable features of the Taj Mahal is the white marble exterior, with the material coming from the quarries of Makrana in Rajasthan.
04:11Transporting these massive blocks, some weighing several tons, to Agra was a huge task.
04:16It was achieved through a network of bullock carts, elephants, and boats,
04:20and once on site, the marble was carved and inlaid with precious and semi-precious stones.
04:25The central dome of the Taj Mahal reaches a height of over 240 feet or 73 meters, and it's a masterpiece of Mughal engineering.
04:33Constructed with a double-shell design, the inner dome maintains the structural integrity, while the outer dome was designed purely for aesthetics.
04:40Masons and engineers used advanced techniques for the time to ensure the dome's perfect symmetry and stability,
04:46including the use of large wooden scaffolding and pulleys to lift the heavy materials into place.
04:51Thought to have involved the efforts of tens of thousands of laborers,
04:54there is no doubt that it's one of the most impressive structures ever built anywhere in the world.
05:0112. The Aqueduct of Segovia, Spain
05:05The Aqueduct of Segovia, which can be seen in the historic city of Segovia in central Spain,
05:10is one of the most impressive examples of ancient Roman engineering that still remain.
05:14Built during the late 1st or early 2nd century during the reigns of Emperor Domitian, Nerva, or Trajan,
05:20its purpose was to transport water to the city from Rio Frio, which is a river around 10.5 miles away.
05:26The Romans were experts at building aqueducts, but the engineering behind ones like this was far ahead of their time.
05:34Constructed mainly from local granite, which provided both durability and structural integrity,
05:38the entire aqueduct was actually built without the use of any mortar,
05:43relying on instead the precise cutting and fitting of the stone blocks to create stability.
05:47Without the ability to use pumps,
05:49the most important step was the preparation, with a survey of the terrain to work out the optimal path for the water channel.
05:56Keeping a consistent and gradual slope that will allow gravity to keep the water flowing.
06:01Roman engineers used a number of techniques to create these gentle gradients, usually around 1%,
06:06to maintain a steady flow of water over long distances without causing any turbulence or stagnation.
06:12The most iconic section of the aqueduct is the series of arches that pass through a plaza in the heart of Segovia.
06:18This section, which reaches a height of up to 60 feet or over 28 meters, is made up of two tiers of arches,
06:24the lower tier with 119 arches and the upper tier with 44.
06:28Each arch was built by assembling precisely cut granite blocks,
06:32held together by the force of gravity and the careful balancing of the stones.
06:36The keystone, which is the central stone at the top of each arch, played a critical role in distributing the weight and ensuring the stability of this structure.
06:45Number 11. The Panama Canal.
06:48Even today, with plenty of alternatives, as much as 80% of the volume of
06:53international trade is transported by ship, meaning that anything that can be done to reduce travel times will have a major impact.
07:01This was even more the case at the beginning of the 20th century, when the U.S. took over a project that was more than
07:07300 years in the making, to build a canal through Central America to provide a significant shortcut.
07:13Designed by the leading engineers of the time, this canal featured a series of locks to lift the ships up from sea level up to
07:19the level of the Gatun Lake,
07:20which is an artificial lake that was created by damming the Chagres River, and then back down to sea level on the other side.
07:27The locks, each measuring 110 feet or about 33.5 meters wide,
07:311,000 feet or about 305 meters long, and 40 feet or 12 meters deep, were vital and needed precision engineering and advanced
07:39construction to be possible.
07:41Excavation of the Galliard Cut,
07:43which is a nine-mile section through the Continental Divide, was one of the most challenging aspects of the entire project.
07:49It required the removal of over 2.7 billion cubic feet or 76 million cubic meters of earth and rock,
07:56which was done with a combination of steam shovels, dynamite, and labor.
08:00Another huge part of the project was the construction of the massive dam which created Gatun Lake,
08:06which became one of the largest artificial lakes in the world at the time.
08:09The dam made from earth and rock was crucial for the canal's water supply and for controlling the flow of water through the locks.
08:16It was finished within 10 years. The canal officially opened on August 15th, 1914,
08:21and was an important moment in global trade and transportation.
08:24The completion of the Panama Canal reduced the sea voyage between the east and west coasts of the United States by approximately
08:318,000 nautical miles, making it one of the greatest engineering achievements of the 20th century.
08:37Number 10. The Akashi-Kaikyo Bridge in Japan.
08:41The Akashi-Kaikyo Bridge, which is also known as the Pearl Bridge, is an impressive structure that connects the city of Kobe on the Japanese
08:48mainland with Owaji Island.
08:51Completed in 1998, it is the world's longest suspension bridge with a central span of 6,532 feet or 1,991 meters.
09:00The idea for the bridge was put forward in the 1950s as weather conditions made the sea crossing unreliable.
09:07Initial planning began in the 1960s and construction work finally began in 1988 after extensive feasibility studies and engineering research.
09:15One of the biggest challenges was the location of the bridge, as the Akashi Strait is a busy shipping route with strong tidal currents
09:22and frequent seismic activity. To be sure that the bridge could withstand these events, engineers use cutting-edge technology and materials within its design.
09:30It, for example, features two massive anchorages built from reinforced concrete which secure the bridge cables on either end and are buried deep into the bedrock.
09:39The main cables, which are essential to the structure of a suspension bridge, were formed from high-strength steel wires.
09:45Each cable is made up of over 36,000 strands of wire,
09:49making them incredibly tough and capable of supporting the weight of an entire bridge deck and the loads from traffic and wind.
09:56The cables were spun on-site using an aerial spinning method where the individual wires were drawn across the strait,
10:02bundled together, and then tightly wrapped to form the final cables.
10:06The bridge incorporates several advanced seismic mitigation features, including dampers and flexible joints, which allow it to withstand earthquakes up to magnitude 8.5.
10:15During the 1995 Kobe earthquake, which happened while the bridge was being built,
10:19it withstood the quake with only minor damage, showing just how effective those features were.
10:24It opened on April 5th, 1998.
10:26The completed bridge is thought to have cost around 3.6 billion dollars, and more than 2 million people were involved at various stages of the project.
10:35Now, transport between Awaji Island and the mainland is far more reliable, and it has transformed the local economies there.
10:43Number 9. The White Pass and Yukon Route Railroad in Canada
10:48The White Pass and Yukon Route Railroad was built during the Klondike Gold Rush to connect the port of Skagway in Alaska to Whitehorse in Yukon, Canada.
10:57It's a narrow-gauge railroad that was completed in the year 1900, and covers a distance of around 110 miles, or 177 kilometers,
11:06through some of the most challenging terrain in the world.
11:08The idea for it came as a need to provide a more efficient route to the Klondike Gold Fields, as existing paths,
11:15such as the Chilkoot and the White Pass trails, were pretty difficult to use.
11:19Construction started in May 1898 and began in Skagway, which was a town that had sprung up almost overnight due to the Gold Rush.
11:26The first major challenge was the steep and rocky terrain of the White Pass,
11:30which required the blasting of rock and the construction of trestles and tunnels to overcome.
11:35The construction workforce was made up of thousands of laborers, including many immigrant workers from Europe and Asia,
11:41and they faced tough working conditions, too, including harsh weather, rough terrain, and the constant risk of avalanches.
11:47But despite all this, they worked tirelessly, often using manual tools and dynamite to carve the route through the mountain.
11:54With, at stages, a series of switchbacks and trestles to climb the steep grade and a cantilever bridge that was, at the time,
12:01the tallest of its type in the world, the railroad reached Lake Bennett in British Columbia in just over a year.
12:07And here, temporary terminus was established.
12:10The final push to Whitehorse continued, and with further tunnels and bridges, the railroad was completed in July of 1900,
12:16just three years after work began.
12:19And it went on to play a critical role in the development of the region,
12:22facilitating the transport of supplies, equipment, and people during and after the Gold Rush.
12:28Number 8. Boeing, Everett Factory in Washington in the United States.
12:34Of all the giant structures that have been built around the world,
12:37the building that has, since being completed, held the world record of being the largest of all, in terms of its total volume,
12:44is the Boeing Everett Factory in Washington.
12:47With the main building having a volume of more than 472 million cubic feet, or over 13.3 million cubic meters,
12:55it's there that some of the world's most renowned aircraft, including the 747, 777, and 787 Dreamliner, are assembled.
13:03Found 25 miles to the north of Seattle, Washington, Boeing first decided to build it after developing the 747,
13:09and needing somewhere to produce it. The location was ideal, due to its closeness to Boeing's Seattle headquarters,
13:15the availability of land, and the nearby Paine Field Airport, which provided essential flight testing and delivery capability.
13:22Work on the factory began in 1967, and it progressed surprisingly fast.
13:26The project involved massive earth-moving efforts, with millions of cubic yards of soil being excavated to prepare the site.
13:33The primary structure of the factory was built using steel frames and large prefabricated panels,
13:38allowing for quick assembly. With the sheer size of the building posing unique engineering challenges,
13:44including the need for a toughened foundation, because of the weight of the building and equipment,
13:48and a roof structure capable of spanning huge distances without interior support columns.
13:54Throughout its history, the Everett factory has undergone several expansions and upgrades. In the late 1980s and early 90s,
14:00it was expanded to accommodate the production of the Boeing 777, a long-range wide-body twin-engine jet.
14:06The most recent major addition to the Everett factory was for the production of the Boeing 787 Dreamliner.
14:12This aircraft, made largely of composite materials, required new manufacturing techniques.
14:17Boeing invested in state-of-the-art assembly technology, including automated fiber placement machines and robotic drilling systems.
14:24This all streamlined the production process.
14:27Moving on to number seven, the Channel Tunnel, UK, France.
14:32Holding the record for having the longest undersea segment of any tunnel in the world,
14:36the Channel Tunnel connects Folkestone in the United Kingdom with Calais in France.
14:41Traveling 31.4 miles or 50 kilometers beneath the English Channel,
14:46taking six years to complete with the efforts of thousands of workers, it was a hugely complicated project to undertake.
14:52The first ideas of a tunnel connecting between the two countries were put forward in the early 19th century,
14:58but serious efforts only began in the mid-20th, once technology available made it realistic.
15:03The modern project began with a treaty between the UK and France in 1986, and construction officially commenced in 1988.
15:10The tunnel itself is made up of three parallel tubes, two for rail traffic and a central service tunnel for maintenance and emergency use.
15:18The twin rail tunnels have a diameter of 25 feet or about 7.6 meters, and all three were constructed using tunnel boring machines,
15:26which are massive mechanical excavators. The construction began at the same time from both the British and French sides.
15:32The tunnel borers were deployed to dig through the earth with crews working around the clock.
15:37These machines not only excavated the soil, but also installed precast concrete lining segments to support the tunnel walls.
15:45One of the trickiest aspects of the project was therefore making sure there was a precise alignment of the tunnels from both sides.
15:52Advanced surveying techniques, including laser guidance systems and satellite positioning, were used to be certain that the two sides would meet in the middle.
16:00The construction faced various challenges, such as managing logistics of transporting materials, dealing with high water pressures, and ensuring worker safety in a confined underwater environment.
16:11Ventilation systems were installed to provide fresh air and remove dust and fumes, while strict safety protocols were implemented to protect the workforce.
16:19The Channel Tunnel officially opened on May 6, 1994, and has significantly reduced travel time and provide a reliable alternative to sea and air routes.
16:29Number six, the Pyramids of Giza, Egypt.
16:33Undoubtedly the most famous and recognizable ancient monuments anywhere on the planet,
16:38the Pyramids of Giza were built during the fourth dynasty of the old kingdom, around 4,500 years ago.
16:44The three pyramids were constructed for the pharaohs Khufu, Khafre, and Menkaure,
16:49with the biggest and most famous, the Great Pyramid of Khufu, being the largest pyramid ever built.
16:54These monumental structures required planning, vast resources, and advanced knowledge of math and engineering to make it a reality.
17:01The site was prepared by leveling the ground, and the ancient Egyptians used a grid system to ensure the base of the pyramid was perfectly square.
17:09This involved laying out a series of right angles using ropes and stakes, and using simple tools like the plumb bob,
17:15and the level to achieve the necessary precision.
17:18The core of the pyramids was made from large blocks of locally quarried limestone,
17:22while the outer casing was made from finer white tura limestone, which gave the pyramids their smooth gleaming appearance.
17:29The stones were transported to the construction site using sledges and rollers, with the Nile River serving as a vital transportation route,
17:36particularly during the rainy season. The exact process with which the heavier stones were put in place still isn't entirely clear,
17:43but it is believed that with some weighing up to 80 tons,
17:46the workers used ramps made of mud brick and limestone chippings to haul them into position.
17:51There are several theories about the ramp system that was used, including straight ramps, zigzagging ramps, or a combination of both,
17:58but the exact method may never be known for certain.
18:01Tens of thousands of workers were involved, and contrary to earlier beliefs, this wasn't forced labor.
18:07Instead, the workforce was made up of skilled tradesmen, craftsmen, and a large number of temporary workers,
18:12possibly recruited from the local population during the agricultural off-season.
18:17They were well-fed and well-treated, and all lived in nearby temporary villages.
18:23Number 5. Rannikot Fort in Pakistan
18:26Rannikot Fort, which is in the Sindh province of Pakistan, is one of the world's largest forts,
18:31often referred to as the Great Wall of Sindh. With a circumference of around 20 miles,
18:37there's surprisingly little we know for certain about the structure.
18:40The fort's construction, history, and purpose remain unknown,
18:43but it's generally believed to have been built during the reign of the Talpur dynasty in the early 19th century.
18:48The main purpose of the fort was likely defensive, as its location along a range provided natural strategic advantages,
18:55with the fort's walls following the contours of the hills and cliffs, making it difficult for attackers.
19:01It would have been a huge challenge to design and build, and require the use of local materials and advanced engineering.
19:07The walls, which are about 33 feet high, vary in thickness, were made using sandstone and limestone quarried from the surrounding area.
19:14The fort's architecture is a strategic design, and it was adapted to the natural landscape.
19:19It features several bastions, gates, and ramparts, which were essential for defense, and has four main gates,
19:25which were constructed with imposing stone arches and were likely reinforced.
19:29One of the more interesting elements of the design is the series of semicircular bastions and watchtowers,
19:34which were placed along the walls to provide vantage points. The bastions are equipped with gun slits, enabling defenders to fire upon attackers,
19:42and the labor force required to build the fort would have been enormous,
19:46probably in the tens of thousands, involving skilled masons, laborers, and possibly artisans from the surrounding area.
19:52And it's also believed to have taken as long as a decade to complete,
19:56thanks to the complexity of the terrain and the huge stone blocks that needed to be lifted into place.
20:02Number four, the Colosseum in Rome.
20:06The Colosseum, officially known as the Flavian Amphitheater, is probably the most iconic structure of ancient Rome.
20:13Constructed under the emperors Vespasian, Titus, and Domitian,
20:16it was completed in AD 80, and became the entertainment center of the city, hosting gladiatorial contests,
20:23sea battles, and public spectacles, and plenty more. Work on it began 10 years earlier under Emperor Vespasian of the Flavian dynasty.
20:30The site chosen for the amphitheater was a flat area in the center of Rome,
20:34where an artificial lake and gardens had been created, as part of Emperor Nero's golden house.
20:40The Colosseum's design relied upon advanced Roman engineering.
20:43The structure is an ellipse, measuring 620 feet long and 512 feet wide, with a base area of 260,000 square feet.
20:51And the main materials used in its construction were travertine limestone, volcanic rock, and brick-faced concrete.
20:58The travertine stones were transported to the site using a sophisticated network of roads and infrastructure,
21:03and the stones were held together without mortar, using iron clamps that were later removed,
21:08which led to the visible pockmarks on the walls you can still see today.
21:12The Colosseum's interior could accommodate between 50,000 to 80,000 people, who were seated according to their social status.
21:19The seating was arranged in a tiered manner, supported by a series of barrel and groin vaults, which provided structural strength,
21:26but also helped with crowd movement. Beneath the arena's floor lay the Hypogeum,
21:30which is a complex underground network of tunnels and chambers, where the gladiators and animals were held before contests.
21:37This area also contained advanced machinery and trapdoors that allowed for dramatic and surprising entrances.
21:45Number three, the Golden Gate Bridge in San Francisco.
21:49The Golden Gate Bridge is a symbol of San Francisco, and it's one of the most recognizable structures in the world.
21:55Covering a distance of 1.7 miles, or 2.7 kilometers, across the Golden Gate Strait, it connects San Francisco to Marin County.
22:04The need for a bridge across the Golden Gate Strait became clear in the early 20th century as the solution to the growing
22:09transportation needs of the San Francisco Bay Area.
22:12Before it, the only practical way to cross the strait was by ferry. The concept gained momentum in the 1920s,
22:18and the decision to build it was made in 1932, with work starting on January 5th, 1933,
22:24amid the Great Depression.
22:26The total cost of the bridge was approximately $35 million, with the suspension bridge design that incorporated Art Deco elements.
22:33Building the Golden Gate Bridge involved overcoming several huge challenges.
22:38The strait's turbulent waters, strong tides, and frequent fog made it really tricky,
22:43and the first major task was completing the two massive towers. Each tower stands about
22:48746 feet, or 227 meters, above the water, and it was built using prefabricated steel sections.
22:54Once the towers were in place, the next phase was spinning the main cables.
22:58These cables are made up of over 27,000 individual wires, totaling 80,000 miles, or 128,000 kilometers of wire.
23:07This process involves spinning the wires back and forth across the strait, using a technique called cable spinning,
23:12which had previously been used, but never on such a scale.
23:16The roadway deck made of prefabricated steel sections was then installed.
23:20These sections were hoisted into place and secured to the suspension cables, completing the main structure.
23:25The final stage involved painting the bridge, both for aesthetic reasons and to protect the steel from corrosion,
23:31with the distinctive international orange color being chosen for its visibility in San Francisco's foggy weather.
23:38The Golden Gate Bridge officially opened to traffic on May 28th, 1937,
23:43following a pedestrian day on May 27th, when 200,000 people walked across it.
23:48Its completion was a huge achievement, and it showed people at the time the possibilities of modern engineering.
23:55Number 2. The Burj Khalifa in Dubai.
23:58Currently holding the world record for being the tallest man-made structure on the planet,
24:03the Burj Khalifa in Dubai reaches an incredible height of 2,717 feet, or 828 meters.
24:10The initial concept of this skyscraper was part of a larger initiative to diversify Dubai's economy from its oil-based routes
24:18towards tourism and luxury. The building's foundations consist of large reinforced concrete mat 12 feet or 3.7 meters thick,
24:26supported by board reinforced concrete piles, each 5 feet in diameter and up to 160 feet deep.
24:33The mat and piles were designed to distribute the building's enormous weight, which reaches about half a million tons,
24:39across the relatively weak soil found in the Dubai region.
24:43The structural system of the Burj Khalifa is a reinforced concrete core with a hexagonal footprint,
24:48surrounded by a series of wings arranged in a Y shape.
24:52This design, known as the buttressed core, was a revolutionary idea, providing stability against lateral forces exerted by wind and seismic activity.
25:01One of the difficulties the engineers found that you may not immediately think of with such a tall building was the pumping of concrete to extreme heights.
25:08This was achieved by using a high-pressure pump system capable of delivering concrete to heights of up to almost
25:142,000 feet, or over 600 meters, a process that set a world record for vertical concrete pumping.
25:21The exterior is made up of reflective glazing, aluminum, and textured stainless steel spandrel panels.
25:27This system was designed to withstand Dubai extreme temperatures, reduce heat absorption, and reduce maintenance requirements.
25:34The spire of the building, which is impressive in its own right, was constructed using a combination of structural steel and aluminum.
25:40It housed communication equipment and was installed in stages, with workers assembling sections on the ground before hoisting them up.
25:47Throughout its construction, the Burj Khalifa relied on the expertise of over 12,000 workers and engineers from around the world.
25:54After six years of construction, it officially opened on January 4th, 2010, and since then, no other building has yet come close to taking its crown.
26:03Number 1. The Great Wall of China
26:07The Great Wall of China is an almost unbelievable structure that stretches over 13,000 miles, or almost
26:1421,000 kilometers, across northern China. Its construction was done in stages across several dynasties,
26:20beginning as early as 2,700 years ago, and it was primarily built to protect Chinese states and empires from various groups from the north.
26:28The earliest sections were built by various states during the Warring States period between 475 and 221 BC.
26:35These initial walls were made of compacted earth and gravel, using local materials.
26:40The aim here was to create barriers against invasions and raids by neighboring states, with these early walls being relatively short and disconnected.
26:48They did, though, lay the groundwork for what would become a massive interconnected defensive network.
26:54The most significant phase of construction began during the reign of the first emperor of China,
26:59Qin Shi Huang, who unified the country in 221 BC.
27:03Recognizing the need for a defense, he ordered the connection and expansion of the existing walls,
27:08which the constructed method during the Qing dynasty involved the use of rammed earth,
27:12which is a technique where the earth was compacted between wooden frames to form solid, sturdy walls.
27:18The construction process here required a massive labor force, which included soldiers, peasants, and prisoners.
27:24It's estimated that hundreds of thousands of people were involved in the building of the wall during the Qin dynasty alone.
27:30The Han emperors employed more advanced construction techniques, incorporating bricks and stones in some sections to improve durability,
27:37and watchtowers and beacon towers were added to enhance communication and military readiness.
27:43The most well-known sections of the Great Wall and those that are seen today were built during the Ming dynasty between
27:491368 and 1644.
27:51After the Ming rulers regained control from the Mongols,
27:54they undertook an ambitious project to rebuild and expand the wall using stronger materials like bricks and granite.
28:01These walls were thicker and higher, with a complex network of watchtowers, garrison stations, and fortresses.
28:07The construction of the Ming Wall was meticulously planned and executed. Workers transported materials using a variety of methods,
28:14including human chains, animals, and machinery. While never exactly being a single continuous wall,
28:21but a series of walls and fortifications built by different dynasties over centuries,
28:25the Great Wall has been the most continuously updated structure in human history,
28:30and one that was vital in helping to strengthen and forge a nation.
28:34Thanks for watching everyone. I'll see you next time. Thank you to our channel members.