Knowledge Base
Buildings, structures, design, materials, and surprising details about the spaces people create.
The Eiffel Tower's iron structure expands and contracts with temperature changes. On a hot summer day it can grow up to 15 centimeters (6 inches) taller than in winter. Sunlight also warms the tower's sides unevenly, causing the top to trace a slow circular arc of about 15 centimeters in diameter across the course of a clear day. Gustave Eiffel accounted for this thermal behavior in the original structural design.
Inside Rome's Pantheon, the interior height equals the diameter of the dome — both just over 43 meters — creating a perfect sphere of space. Built around 125 AD, its unreinforced concrete dome held the record as the world's largest for over 1,300 years, until Brunelleschi's dome for Florence Cathedral was completed in 1436. The oculus at the top — 8.92 meters across — is the building's only source of natural light, and the floor is slightly curved to drain rainwater that falls through it.
The Sydney Opera House roof is covered with 1,056,006 ceramic tiles. Its shell shapes were derived from the surface of a sphere, allowing the complex curves to be expressed through a shared geometry.
Burj Khalifa reaches 828 meters, or 2,716.5 feet, above Dubai. The building has 200 floors in total, including 160 habitable stories.
Roman marine and architectural concrete has survived in harsh environments for over two thousand years due to “lime clasts”—small mineral inclusions formed by hot-mixing quicklime. When moisture or seawater seeps into microscopic fissures, it reacts with these lime clasts to dissolve and recrystallize as calcium carbonate, sealing the cracks before they can expand.
Construction of Pisa’s famous bell tower began in 1173 on an unstable foundation of sand, clay, and river silt only three meters deep. The tower began leaning by the time masons reached the third floor in 1178. Successive builders tried to compensate by making columns and arches slightly taller on one side on the upper floors, resulting in a building that is actually curved like a banana.
The four minarets framing the Taj Mahal in Agra, India, were deliberately constructed with a slight outward tilt rather than standing perfectly perpendicular. This structural safeguard ensures that in the event of a catastrophic earthquake, the heavy stone towers will collapse safely away from the central dome and mausoleum rather than crashing through the roof.
Modern skyscrapers are engineered to sway in high winds rather than stand rigid. A building that cannot flex would accumulate stress until it fractured. The Empire State Building sways up to 1 inch (2.5 cm) at its top in a strong wind; the Burj Khalifa in Dubai, the world's tallest building, is designed to sway up to 1.5 meters at its pinnacle under wind load conditions.
The Great Wall of China was not built at once — it evolved over more than two millennia. Construction began during the 7th century BC and continued through the Ming Dynasty (1368–1644 AD), which built the most famous sections still visible today. Different emperors, armies, and dynasties each added or rebuilt sections, resulting in a total system of walls, trenches, and natural barriers stretching over 13,000 miles in total length.
The White House in Washington, D.C. contains 132 rooms across six stories, including 35 bathrooms, a tennis court, a bowling alley, a putting green, a jogging track, a swimming pool, and a private movie theater. Originally completed in 1800, it has been continuously renovated and expanded over the centuries and is considered both a working office and an official residence.