For nearly four thousand years, the Great Pyramid of Giza was the tallest human-made structure on earth.
At 147 meters tall, the pyramid has impressive height.
But it looks puny next to the tallest human-made structures today:
skyscrapers.
Every day in cities around the world, millions of people go to work in towers made of steel and glass.
These modern structures demonstrate the best in construction technology and engineering skills.
Modern cities surely could not function without them.
People first began building skyscrapers in the nineteenth century.
Many cities were rapidly growing, and space in downtown areas was in high demand.
There was nowhere to build but up, so smaller buildings were demolished and replaced by taller buildings.
But the heights of these tall buildings were limited by the materials and technologies of their time.
Before skyscrapers, tall structures were rarely built for people to live or work in.
Few buildings were taller than five stories because people had to climb so many stairs.
Elevators at the time were meant for freight, not people.
They were seen to be unsafe.
If the cable that held the elevator snapped, the elevator would fall, killing those inside.
In 1852 Elisha Otis invented the safety elevator, which solved the problem of how to transport people up and down tall buildings.
Otis' new safety elevator had mechanical locks that automatically held the elevator firmly in place if the cable snapped.
While Elisha Otis was improving the elevator, other inventors were hard at work improving water pumps.
As cities expanded and their suburbs grew, more powerful pumps were needed to provide water to distant areas.
Eventually pumps were invented that could supply water across greater horizontal distances.
They were also powerful enough to pump water vertically to greater heights.
These pumps were essential for skyscrapers, which needed efficient plumbing.
Another factor that limited a building's height at the time were building materials.
Traditional materials like stone and brick were too heavy.
When stone or brick layers are piled too high, their combined weight will crush the bottom layers.
Wood was light but lacked the necessary strength.
Steel was an ideal material. With steel beams, buildings could be built around a metal frame instead of stone walls.
Finally in the 1850s, manufacturers developed a process for mass-producing steel.
This made steel available in the quantities needed for a skyscraper.
With these inventions, buildings soared higher than ever before.
But architects and engineers hadn't solved every design problem.
The design and construction of new buildings brought unforeseen challenges.
For example, strong winds could cause a tall building to sway back and forth.
Designers eventually built a strong central core of steel around the main elevator shaft of a building.
This prevented the building from shaking.
The core also made the skyscraper stable and more rigid.
Windows were another challenge because ordinary glass presented a danger.
If a window broke, large pieces of sharp glass would fall to the ground and injure people below.
The invention of tempered glass, or safety glass, solved this problem.
Safety glass was stronger than ordinary glass, and when it broke, it shattered into small pieces with rounded edges.
By the twentieth century, New York City was famous for its skyscrapers.
The city's skyline was continually being changed by the race to build the tallest skyscraper.
In 1930 the 283-meter Bank of Manhattan Building became the tallest building in the world.
It was taller than the rival Chrysler Building, which was still under construction.
However, the surprise addition of a tall spire to the Chrysler Building increased the building's height to 319 meters.
The Chrysler Building gained the title of the world's tallest building.
The Bank of Manhattan Building had only held the distinction for a month.
But the Chrysler Building's record was not undisputed.
The spire and many of the Chrysler Building's top floors were unoccupied.
But the Bank of Manhattan Building's highest occupied floors were higher than those in the Chrysler Building.
Some argued that the Bank of Manhattan Building still held the record.
By 1931 the arguments on both sides became pointless when the Empire State Building was completed.
At 443 meters tall, it was undeniably the tallest building in the world.
Its record was not broken until 1972.
New skyscrapers are still being built all over the world.
Though not world-record breakers, skyscrapers over five hundred meters tall have been built in China, Korea, and the Middle East.
In 2009 the 828-meter tall Burj Khalifa in Dubai became the tallest building in the world.
Thanks to advances in materials and technology, today's skyscrapers stand many times higher than the giant Egyptian pyramids.
And architects and engineers keep dreaming about even taller structures.
Future human-made structures will likely reshape the urban landscape—just as the first skyscrapers did over a hundred years ago.
