Formatted Contents Note: The technology behind amazing built structures -- How did the Egyptians build the pyramids? -- What is Stonehenge and how was it built? -- Which is the longest wall in the world? -- Who carved four US presidents into a mountain? -- What is the Christ the Redeemer statue made from? -- Why was the Eiffel Tower built? -- Has the Statue of Liberty always been green? -- How was the Hoover Dam built? -- Why does the Gateway Arch sway in the wind? -- Whose idea was it to tunnel between Britain and France? -- How can the Akashi-Kaikyo Bridge withstand earthquakes? -- Which is the tallest building in the world? -- How long does it take for the London Eye to complete one revolution?.