10 of History’s Most Expensive Megaprojects

Civilizations throughout history have been fascinated with building large things, whether they are monuments, public works, religious structures, or engineering marvels. None of them, however, compare to modern megaprojects.

Thanks to advances in architecture, building materials, machinery, and countless other technological fields over the past century, today’s megaprojects far surpass anything constructed in the past, both in scale and in cost.

Today, we’re counting down some of the most expensive megaprojects in modern history. Whether they were built to explore the universe, move millions of people, or reshape entire regions, every one of them required budgets measured in billions of dollars.

Related: 10 Ambitious Projects Aimed at Resurrecting Extinct Animals

10 Large Hadron Collider

The Large Hadron Collider (LHC) is located near Geneva, Switzerland, along the Franco-Swiss border. Often described as one of the most ambitious scientific projects in history, the circular particle accelerator spans approximately 17 miles (27 km) and is equipped with superconducting magnets and complex accelerating structures. Construction took roughly a decade to complete, with costs totaling several billion dollars. The collider was designed to study fundamental particles found throughout the universe, particularly theoretical particles such as the Higgs boson.

The LHC operates by accelerating protons to nearly the speed of light using an intricate system of supercooled magnets. It consumes roughly 120 megawatts of electricity, comparable to the energy use of a small city. The facility represents one of the largest international scientific collaborations ever attempted, involving thousands of scientists and engineers from more than 100 countries.

Its most famous achievement came in 2012 with the confirmation of the Higgs boson, a particle whose existence had been predicted nearly 50 years earlier. Beyond particle physics, the LHC demonstrates how modern megaprojects often require not only enormous construction budgets but also decades of international cooperation and ongoing operational investment.^[1]

9 James Webb Space Telescope

The James Webb Space Telescope was launched in late 2021 after years of development and total project spending exceeding $10 billion. Its ability to observe infrared light distinguishes it from its predecessor, the Hubble Space Telescope, allowing scientists to look farther back in time than ever before. This capability enables studies of the first galaxies, the evolution of cosmic structures, the birth of stars, and the potential for life on distant worlds.

Although NASA led the project, the telescope represents a major international collaboration involving the European Space Agency and the Canadian Space Agency. Scientists from around the globe compete for observation time through a rigorous peer-review process, making Webb one of the most important shared scientific resources in operation today.

The project’s budget changed dramatically over time. Originally projected to cost around $1 billion and launch in 2010, repeated delays and technical challenges pushed both the timeline and expenses far beyond initial expectations. Despite the overruns, the telescope has already produced some of the most detailed and scientifically valuable images ever captured of the universe.^[2]

8 Abraj Al-Bait Clock Tower Complex

Officially known as the Abraj Al-Bait, the Makkah Royal Clock Tower complex is one of the largest and most expensive building projects ever completed. Comprising seven towers, the complex contains hotels, shopping centers, residential apartments, prayer facilities, and numerous other amenities. The development is government-owned and forms part of the King Abdulaziz Endowment Project.

The centerpiece of the complex is the central tower, which rises approximately 1,970 feet (600 m) into the sky. Its enormous clock faces—among the largest in the world—are visible from miles away and have become one of the defining features of Mecca’s skyline.

Construction began in 2004 and concluded in 2012 at a reported cost of roughly $15 billion. The project generated controversy because it required the demolition of the 18th-century Ajyad Fortress, a historic Ottoman structure. Critics argued that an important cultural landmark was sacrificed to make way for modern development. Regardless of the debate, the complex remains one of the most expensive and recognizable architectural projects ever undertaken.^[3]

7 Channel Tunnel

Also known as the Eurotunnel, the Channel Tunnel consists of three tunnels connecting the southern coast of England with northern France beneath the English Channel. The system stretches approximately 31 miles (50 km), making it one of the longest undersea transportation tunnels ever constructed.

Completed in 1994, the project created a permanent rail connection between Great Britain and continental Europe. Construction required vast quantities of steel and concrete, as well as years of engineering work beneath the seabed. While original estimates were significantly lower, the final cost climbed to the equivalent of more than £20 billion.

One of the tunnel’s most important safety features is the service tunnel running between the two main rail tunnels. Designed as an emergency escape route, it proved its value shortly after opening when passengers safely evacuated during a tunnel fire. Today, the Channel Tunnel remains one of the most impressive transportation infrastructure projects ever completed and has fundamentally changed travel between Britain and mainland Europe.^[4]

6 Big Dig Project

The Big Dig, officially known as the Central Artery/Tunnel Project, was designed to reduce traffic congestion and improve transportation in Boston, once considered one of the most congested cities in the United States. The project involved replacing the elevated section of Interstate 93 with an underground highway system while extending Interstate 90 to Logan International Airport.

The undertaking required the construction of multiple tunnels beneath one of America’s oldest cities, creating extraordinary engineering challenges. Three primary tunnels were built, including a dedicated service tunnel designed to function as an emergency escape route. Throughout construction, crews had to work around existing buildings, utilities, roadways, and public transit systems.

Although completed years ago, the Big Dig remains one of the most expensive highway projects ever undertaken. Initial estimates were dramatically exceeded, and when financing costs and related commitments are included, the project’s total price tag is expected to surpass $24 billion by the time the final bonds are paid off in 2038. Despite the controversy surrounding its cost, the project permanently transformed transportation throughout the Boston metropolitan area.^[5]

5 Three Gorges Dam

The Three Gorges Dam stands as one of the largest engineering projects in Chinese history. Built along the Yangtze River, construction began in 1994 with the goal of creating the world’s largest and most powerful hydroelectric facility. Measuring approximately 610 feet (185 m) in height and 1.3 miles (2.3 km) in width, the dam is paired with a massive reservoir extending nearly 400 miles (644 km) upstream, dramatically reshaping the surrounding landscape.

The project was designed to generate enormous quantities of electricity, improve navigation for 10,000-ton freighters traveling through China’s interior, and reduce the devastating floods that had plagued the Yangtze basin for centuries. The scale of the undertaking required the relocation of entire communities and the reconstruction of infrastructure across a vast region.

Originally estimated to cost around $28.6 billion, the final expense exceeded $37 billion, with construction taking nearly two decades to complete. More than one million people were displaced during the process, making it one of the largest resettlement efforts ever associated with a construction project. Despite ongoing environmental and social concerns, the Three Gorges Dam remains one of the most influential infrastructure projects of the modern era.^[6]

4 International Thermonuclear Experimental Reactor (ITER)

The International Thermonuclear Experimental Reactor, better known as ITER, is one of the most ambitious energy projects ever attempted. Located in southern France, the facility is designed to demonstrate the feasibility of commercial fusion power—a technology that, if successfully developed, could provide vast amounts of energy with minimal environmental impact.

Unlike conventional nuclear power plants, which generate energy through fission, ITER seeks to produce energy through fusion, the same process that powers the Sun. The project represents a collaboration among dozens of countries, including members of the European Union, the United States, China, India, Japan, Russia, and South Korea.

Since construction began in 2007, the project has faced repeated delays and escalating costs. Early estimates placed the price tag at roughly $22 billion, but more recent projections have pushed total costs to approximately $65 billion. Despite the challenges, supporters argue that the potential rewards justify the expense. If successful, ITER could fundamentally change how humanity generates electricity in the future.

Although the facility is not yet operational, it remains one of the most expensive scientific and engineering megaprojects ever undertaken.^[7]

3 Beijing-Shanghai High-Speed Railway

The Beijing-Shanghai High-Speed Railway connects two of China’s most important economic centers. Stretching approximately 820 miles (1,318 km), the line was built to dramatically reduce travel times between Beijing and Shanghai while increasing transportation capacity along one of the busiest corridors in the country.

Construction began in 2008 and was completed in 2011, an astonishingly short timeline for a project of this scale. The railway reduced travel times between the two cities from roughly 14 hours to about 5 hours. It was designed to accommodate hundreds of thousands of passengers every day.

Trains operating on the route routinely exceed speeds of 230 mph (370 km/h), placing the line among the fastest rail systems in the world. Construction required 244 bridges and 22 tunnels, including the Danyang-Kunshan Grand Bridge, which at approximately 102 miles (164 km) remains the world’s longest bridge.

The total project cost reached approximately 220.9 billion yuan, or roughly $32 billion. Since opening, the railway has become one of China’s most successful transportation investments, carrying millions of passengers annually while generating substantial revenue.^[8]

2 Airbus A380

The Airbus A380 program was once viewed as the future of long-distance air travel. Developed by the European aerospace giant Airbus, the double-decker aircraft was designed to carry up to 615 passengers while providing airlines with unprecedented capacity on major international routes.

The project required years of research, development, testing, and manufacturing investment. Engineers faced numerous technical challenges, including integrating complex wiring systems, improving fuel efficiency, and coordinating production across multiple European countries. Costs continued to rise as delays and redesigns pushed the program further beyond its original budget.

Although the aircraft became an engineering marvel and remains beloved by many passengers, the aviation industry gradually shifted toward smaller, more fuel-efficient long-range aircraft. This change reduced demand for the A380 and limited its commercial success. The COVID-19 pandemic accelerated the trend, making the giant airliner even less attractive to many carriers.

By the time production ended, the A380 program had cost an estimated €30 billion, or approximately $33.9 billion. While the aircraft never achieved the commercial dominance Airbus once envisioned, it remains one of the most ambitious and expensive aerospace projects ever completed.^[9]

1 International Space Station

The International Space Station is one of humanity’s greatest engineering achievements and perhaps the ultimate example of a modern megaproject. Construction began in 1998 and required unprecedented cooperation among the United States, Russia, Canada, Japan, and multiple European nations.

The station provides a combined living and working space roughly equivalent to two Boeing 747 aircraft and remains the largest human-made structure ever assembled in orbit. Building it required 45 major assembly missions, including 36 American Space Shuttle launches and nine Russian launches, along with approximately 1,705 hours of spacewalks.

Orbiting Earth every 90 minutes, the ISS passes over more than 90% of the world’s population. Beyond serving as a symbol of international cooperation, it functions as a scientific laboratory where astronauts conduct research into biology, physics, medicine, materials science, and the long-term effects of living in space.

The station’s assembly cost is commonly estimated at around $100 billion. However, some calculations place the total investment even higher when operational expenses are included. Regardless of the exact figure, no other space-based construction project comes close. More than a quarter-century after construction began, the International Space Station remains one of the most expensive and ambitious megaprojects ever undertaken by humanity.^[10]