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The inscription on the Pantheon's portico credits Marcus Agrippa, but his temple on the Campus Martius burned in 80 AD, Domitian's rebuild burned in 110 AD, and the domed building standing today went up under Trajan and Hadrian between 114 and 126 AD. Hadrian kept Agrippa's name to signal continuity with Augustus, a move that fooled even Cassius Dio. Inside, the floor to the oculus and the width of the rotunda both measure 43.3 meters, so a perfect sphere fits within. The 4,500-ton dome stands with no steel reinforcement thanks to pozzolana mortar and aggregate that shifts from heavy travertine at the base to terracotta, tufa, and finally floating pumice near the 9.1 meter oculus, all over 6.4 meter walls hiding chambers and relieving arches.

Out front, 16 granite columns of 60 tons each were cut at Mons Claudianus in Egypt, dragged across the desert, floated down the Nile on the spring flood, shipped to Ostia, and hauled up the Tiber. A ghost roofline above the porch suggests 50 Roman foot columns were planned; only 40 foot shafts arrived, a mismatch studied by Mark Wilson Jones and Rabun Taylor. In 609 AD the Byzantine emperor Phocas gave the building to Pope Boniface IV, which saved it as a church. Constans II stripped its gilded bronze roof tiles in 663, Pope Urban VIII melted the portico's bronze trusses mostly into cannons for Castel Sant'Angelo, and twin bell towers mocked as the ass's ears stood until the late 19th century. Raphael and Italy's first kings are buried inside.

• Why Livy's rule of one god per temple, for lightning strikes, makes the name Pantheon likely a nickname
• Modern analysis showing uniform concrete would have put 80 percent more stress on the dome's arches
• The oculus as a reverse sundial and the sloped floor whose ancient drains still carry away the rain
• The Roman pasquinade: what the barbarians did not do, the Barberini did
• Brunelleschi's Florence dome and Jefferson's University of Virginia rotunda as descendants of the design

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In 1406 the Yongle emperor of the Ming dynasty moved China's capital from Nanjing to Beijing and ordered a new palace that took 14 years and more than a million workers to build. Its name, the Purple Forbidden City, tied the emperor's home to the North Star, the Ziwei Star, seat of the Jade Emperor. Builders dragged Phoebe zhennan logs out of malaria-ridden jungles in southwestern China and paved the halls with golden bricks from Suzhou, fired for over 130 days and soaked in tung oil until they rang like metal. Behind an eight meter wall, a 52 meter moat, and the Meridian Gate, only the emperor could walk the Imperial Way to the Hall of Supreme Harmony, nine bays wide and five deep.

Life in the inner court followed yin and yang, trigrams from the I Ching, and a rigid ranking of consorts in the six Eastern and six Western palaces. The Yongzheng emperor, out of respect for the Kangxi emperor, moved his bedroom to the smaller Hall of Mental Cultivation, which ran the empire for two centuries. After 24 emperors, Puyi abdicated in 1912 but kept living in the inner court until a 1924 coup; the Palace Museum opened in 1925. In 1933 curators fled the Japanese advance with thousands of crates, and the collection ended up split between Beijing, Nanjing, and Taipei. During the Cultural Revolution, Zhou Enlai sent a battalion to guard the gates, and in 2019 some 19 million people walked through them.

• The myth of 9,999 rooms versus the surveyed count of 8,886 bays, each defined by four wooden pillars
• A 200-ton carved marble ramp slid to the palace in winter over roads flooded from wells to form ice
• The mirror hung above the throne, said to fall and crush any illegitimate usurper who sat beneath it
• Black roof tiles on the library to invoke water against fire, and green tiles for the crown prince's youth
• More than a thousand jeweled clocks, many from Britain, and a full-size replica built at Hengdian World Studios

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In September 1812 Napoleon's retreating troops rigged the Alhambra with explosives and blew up eight towers before a Spanish soldier, José García, cut the remaining fuses. The name comes from the Arabic for the red one, after walls of rammed earth made from iron-rich clay. The hill held Roman, Visigothic, and ninth century military works before Muhammad I, founder of the Nasrid dynasty, made it his capital in 1238. The Nasrids brought water up with the Sultan's Canal, a gravity-fed system tapping the river miles upstream, and guarded it with the Alcazaba citadel. In the 14th century Yusuf I and Muhammad V built the Comares Palace and the Palace of the Lions, directed by viziers and poets such as Ibn al-Khatib and Ibn Zamrak.

In January 1492 the last Nasrid sultan surrendered the city to Ferdinand and Isabella without a siege. That March they signed the Alhambra Decree expelling Spain's Jews, and in April Columbus pitched his voyage in the Hall of Ambassadors. In 1526 Charles V tore out part of the Comares Palace for a heavy Renaissance palace. By the 18th century squatters, prisoners, and sheep filled the courtyards, and an earthquake struck in 1821. Washington Irving moved in and published Tales of the Alhambra in 1832, making the ruin famous. The Contreras family then restored it to match tourist fantasies, until Leopoldo Torres Balbás arrived in 1923 and applied scientific preservation.

• A fortified tunnel called a coracha that let soldiers reach the river for water during a siege
• Courtyards aligned north to south so winter sun warmed the halls while deep porticoes blocked the summer sun
• Muqarnas ceilings and walls of poetry carrying the Nasrid motto, there is no victor but God
• Seventy empty tombs left in the royal mausoleum after the departing sultan took his ancestors' remains into exile
• Rafael Contreras's invented Persian-style domes on the Court of the Lions, later dismantled by Torres Balbás

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Pisa's bell tower started with a widow, Donna Berta di Bernardo, who left 60 soldi in her will in 1172 for its first stones. Construction began in August 1173 on a foundation just three meters deep, set in soft clay, sand, and shells, and by 1178 the tower was sinking at the second floor. Wars with Genoa, Lucca, and Florence then halted work for nearly a century, which gave the soil time to compress. In 1272 Giovanni di Simone built the new floors taller on the low side to correct the tilt, adding weight where it was already sinking and leaving the tower curved like a banana. It took 199 years to finish, with Tommaso di Andrea Pisano adding the bell chamber, and the original architect is still debated.

The finished tower held seven bells, including one from 1262 that rang for executions such as that of Count Ugolino in 1289. The Galileo cannonball story rests only on a biography by his pupil Vincenzo Viviani. In World War II US Army Sergeant Leon Weckstein, sent to see whether Germans were using it as a lookout, was so struck by the square that he never called in artillery. By 1990 the lean hit 5.5 degrees, and after a deadly tower collapse in Pavia the year before, Pisa closed it on January 7, 1990. Engineers removed about 38 cubic meters of soil from under the high side, bringing the tilt back to its 1838 position, and in 2008 declared that it had stopped moving.

• A bronze fragment bearing Bonanno Pisano's name, found in 1820, that may be debris from cathedral doors burned in 1595
• A 2001 study pointing to Diotisalvi, builder of the San Nicola bell tower and the Pisa Baptistery
• The government's mandate for the 1990s rescue: save the tower but keep the lean
• Steel cables, 870 tons of lead counterweights, and slow soil extraction instead of jacking up the low side
• The 2018 finding that the soft soil keeps the tower from resonating with earthquakes, protecting it from at least four since 1280

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In 1812 the Swiss traveler Johann Ludwig Burckhardt, disguised as a local and leading a goat to sacrifice at the tomb of Aaron, walked through the narrow Siq and into Petra. The basin gets only about 7.6 inches of rain a year, yet it was settled by Neolithic farmers at Beidha around 7000 BC and later by the Edomites. In the fourth century BC the Nabataeans, a nomadic Arab tribe, made it their city of Raqmu, a choke point on incense routes linking Gaza, Damascus, and the Persian Gulf. They dammed the flash floods, cut a 280 foot tunnel to send the water around the city, and ran ceramic pipes at a steady four degree slope to feed cisterns and sell water to caravans.

The wealth went into rock-cut monuments like the 121 foot Treasury, an 8,500 seat theater, and a garden with a public swimming pool. Rome annexed the kingdom in 106 AD as Arabia Petraea, and under Byzantine rule the Urn Tomb became a church. More than 140 carbonized papyri from a sixth century church show a family around the archdeacon Theodoros suing over property and inheritances as the incense trade moved to the Red Sea. The earthquake of 363 broke the water system, and the city emptied. The Bdoul Bedouin lived in the tombs until they were relocated in the 1980s, and after its 2007 New Seven Wonders listing Petra passed one million visitors in 2019.

• Why nomadic knowledge of desert water made the Nabataeans skilled hydraulic engineers
• Bullet holes in the Treasury's stone urn from Bedouin who believed a pharaoh's gold was hidden inside
• Castor and Pollux, Egyptian obelisks, and the goddess Isis-Tyche on the facades as signals to foreign merchants
• Salt weathering, where moisture from millions of visitors crystallizes salt that flakes the carvings away
• An Olympic stadium-sized platform half a mile south of the city center, spotted by satellite and drones in 2016

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Around 1264 BC Ramesses II had two temples cut into a sandstone cliff in Nubia at the second Nile cataract, a statement of power over a region rich in gold and ivory. The Great Temple's facade holds four seated statues of the pharaoh, each 66 feet tall, with his family carved no higher than his knees. Its axis was set so that twice a year, on dates recorded as October 22 and February 22, the rising sun reached the inner sanctuary and lit Ra-Horakhty, Amun, and the deified Ramesses while leaving Ptah in shadow. The Small Temple, for Hathor and Queen Nefertari, shows her statues at the same height as his. Sand then buried the site until Johann Ludwig Burckhardt spotted a head in 1813 and Giovanni Belzoni dug in 1817.

In 1959 Egypt announced the Aswan High Dam, and Lake Nasser was set to rise up to 200 feet and dissolve the porous sandstone. Proposals ranged from a glass bubble with underwater viewing galleries to an $82 million protective dam to jacking the temples up whole. The Swedish firm VBB won with a plan to cut them apart and rebuild them higher. Behind an 89 foot cofferdam, workers injected epoxy into the stone for seven months, and marble cutters from Carrara used hand saws to slice both temples into 1,036 blocks. The temples were rebuilt 682 feet inland and over 213 feet higher, finished in 1968 ahead of schedule for just over $41 million from 48 countries, an effort that led to the UNESCO World Heritage List.

• Local workers who refused European coins until Belzoni convinced a sheikh they could be traded upriver
• Champollion's thermometer reading of over 125 degrees Fahrenheit inside the buried temple
• 34,000 tons of sand piled against the facade as a cushion while 300,000 tons of cliff above were chipped away
• The face of one Ramesses statue moved separately after its crown was sawn off
• Concrete domes and rubble used to build an artificial mountain over the rebuilt temples

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The story starts in the Circus of Nero, where tradition holds the Apostle Peter was crucified upside down around 64 AD and buried in a simple plot on Vatican Hill. Constantine built Old St. Peter's over the grave in the fourth century, and by the 15th century its walls were leaning. In 1505 Pope Julius II decided to demolish it for a new church big enough for the tomb he had commissioned from Michelangelo. Paying for it meant selling indulgences, and the German friar Johann Tetzel's aggressive sales campaign provoked Martin Luther and the Protestant Reformation. Bramante laid the foundation stone in 1506, but Raphael, Peruzzi, and Sangallo kept redrawing the plans, Rome was sacked in 1527, and Bramante's piers began to crack.

Michelangelo took over in 1547, in his 70s, simplified the design, and replaced a hemispherical dome with a taller ovoid dome on 16 ribs that pushed its weight down into the piers instead of outward. Under the Counter-Reformation, Carlo Maderno stretched the church into a Latin cross with a long nave and a broad facade that hides the lower dome from the square. The shell was finished in 1626, 120 years after it began. Bernini then spent some 50 years making the space readable, with the bronze baldacchino nearly 30 meters tall and the Cathedra Petri. In the 2020s a Vatican partnership with Microsoft mapped the basilica from over 400,000 drone photos and rebuilt it in Minecraft for the 2025 Jubilee.

• Why a Pantheon-style dome on four standalone piers would have burst, and how an egg shape solved it
• The twisted columns of the baldacchino, modeled on ancient columns Constantine brought from the Temple of Jerusalem
• Moving the 360 ton obelisk from Nero's circus in 1586 with 44 capstans, 900 men, and 75 horses under an order of total silence
• Benedetto Bresca, the sailor who broke the silence to shout water on the ropes, and the Palm Sunday privilege his hometown won
• Cherubs that look normal-sized from the nave but stand over two meters tall

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The tower began in 1884 as a sketch by two engineers at Gustave Eiffel's firm, Maurice Koechlin and Émile Nouguier, for the 1889 World's Fair marking the centennial of the French Revolution. Architect Stephen Sauvestre added the arches and glass pavilion, and Eiffel bought the patent and put up half the capital. One financier, the bank CIC, was profiting from loans tied to an indemnity imposed on Haiti. Paris's artistic elite, including Opera architect Charles Garnier, formed the Committee of 300 against it. Work began in January 1887 with pressurized caissons sunk 22 meters into the riverbank mud, and 18,038 parts and 2.5 million rivets went up with a one millimeter tolerance. Only one of about 300 workers died.

Nearly two million people visited during the fair, but the land deal meant the tower would revert to the city and could be scrapped in 1909. Eiffel made it indispensable as a laboratory and antenna. In 1910 Father Theodor Wulf measured higher radiation at the top than the bottom, early evidence of cosmic rays, and the tower broadcast time signals. In 1914 it jammed German radio at the First Battle of the Marne, and in 1917 it intercepted the message that led to Mata Hari's arrest. In 1940 the French cut the elevator cables before the occupation, and in 1944 General von Choltitz ignored Hitler's order to destroy it.

• The curved legs calculated so sideways wind becomes downward compression into the foundations
• Otis hydraulic elevators on inclined tracks, powered by a water reservoir on the second level
• Guy de Maupassant eating lunch at the tower daily because it was the one place in Paris he could not see it
• German soldiers climbing the stairs twice after the wind tore away their oversized flag
• Puddle iron that tilts the top up to 18 centimeters away from the sun, and a copyright on the nighttime lighting

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The CN Tower was built for television, not tourists. In the late 1960s and early 1970s, new glass skyscrapers like First Canadian Place blocked the rooftop microwave links Toronto relied on and bounced broadcast signals into ghosting and static. The Canadian National Railway set out to build a communication hub taller than anything in the city. Construction began in February 1973 with 56,000 tons of earth removed and a 6.7 meter thick foundation. A hydraulic slip form rose about six meters a day, and engineers kept it true by watching hanging plumb bobs through telescopes with crosshairs. Over 553.3 meters the tower strays from vertical by only 29 millimeters.

A Sikorsky S-64 Skycrane nicknamed Olga flew the 102 meter antenna up in 36 pieces, cutting a six month crane job to three and a half weeks. The design shifted along the way, from a three-pillar tripod to a hexagonal core, and added a higher observation pod nicknamed Bud's Bubble. Tourism paid off its roughly 63 million Canadian dollar cost in 15 years. It drew stuntmen Dar Robinson and Dan Goodwin, a 2,579 step stair climb record of 7 minutes 52 seconds, the glass floor in 1994, and the EdgeWalk in 2011. It held the world's tallest freestanding structure title for 32 years until the Burj Khalifa passed it in 2007.

• Dar Robinson's 1979 parachute jump opened three seconds before impact, and his 1980 jump on a wire decelerator with no parachute
• Falling ice that closed the Gardiner Expressway in 2007 and punctured the Rogers Centre roof in 2018
• The fire safety redundancies officials pointed to after the 2000 fire at Moscow's Ostankino Tower
• The tower versus building distinction that let Guinness certify it as the tallest freestanding tower after 2007
• Over 1,300 LED lights that change color for events and dim during bird migrations

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In 1910 Frank W. Woolworth, rich from his five and ten cent stores, planned an ordinary 12 to 16 story headquarters in lower Manhattan. Then on a trip to Europe, people kept asking him about the Singer Building instead of his stores, and his plans exploded to 30, then 45 stories, with a minimum height of 750 feet. His architect Cass Gilbert pushed it to 792 feet and 60 stories so the tower would not look stubby on its wide base. Woolworth wanted something like the Palace of Westminster clad in granite; Gilbert won with lighter, fireproof glazed terracotta and a U-shaped base that put every office within 10 feet of a window. Contractor Louis J. Horowitz saw ego behind every decision.

Woolworth's 24th floor office was done in French Empire style, with green marble walls, a desk with hidden buttons to summon staff, and portraits of Napoleon, one of which he replaced with a portrait of himself. On April 24, 1913, President Woodrow Wilson pressed a telegraph button in Washington that lit the tower for 900 guests on the 27th floor. By 1914 Woolworth owned it outright, and the bank paid him $100,000 a year to lease its offices. After his death in 1920, his heirs took a $3 million mortgage to pay inheritance taxes and had sold out by 1924. By the 1970s rusting steel was pushing terracotta blocks off the facade, and today the top 30 floors are luxury condominiums.

• Woolworth asking the construction firm to manage the project for free, and being charged its $300,000 fee anyway
• Window counts that range from 2,843 to 5,000 depending on the source
• Darker glaze on the upper terracotta panels to cancel out the fading effect of distance
• The relay that let a button in the White House switch on roughly 80,000 bulbs in New York
• Rust jacking, freeze cycles, and the metal netting hung to protect pedestrians from falling terracotta