Spheres & Domes
A dome is a self-supporting structural element of architecture that resembles the hollow upper half of a sphere. Despite their thinness, domes are some of the strongest and stiffest structures in existence today.
A sphere is a geometrical object that is a 3D analogue to a 2D circle. The Earth is often seen as a sphere in geography, and the celestial sphere is an important concept in astronomy. Manufactured items including pressure vessels and most curved mirrors and lenses are based on spheres. Spheres roll smoothly in any direction, so most balls used in sports and toys are spherical, as are ball bearings.
The carvings adorning the sphere are mysterious and mystical. Most agree the human figure is a depiction of Helios, the god of the Sun. He sits atop a grand throne, clutching a whip in one hand and three lit torches in the other. A great beast rests at his feet, which is said to be either a lion or a dog and is thought to represent a constellation.
Before domes, there were rectangular buildings. Almost all ancient buildings had roofs supported by forests of columns. The columns prevented the heavy roofs from collapsing, but they left very little open interior space. The Parthenon in Athens is an example of this design.
Around 100 A.D., Roman builders rotated an arch in a circle and discovered that it created a strong three-dimensional shape: the monolithic dome. So, they began capping churches and mosques with this new and brilliant design.
Rome's Pantheon is remarkable for its size, its construction, and its design. The enormous dome stretches 43 mtrs in diameter. Given the dome's size and weight, Emperor Hadrian's engineers had to find ways to lighten the heavy structure. They scooped out 140 waffle-like depressions, called coffers, in five rows around the dome's base to eliminate some masonry and reduce the dome's weight. They also carved an opening, called an oculus, at the top of the dome, which reduced some mass and created a daily light show for which the Pantheon is famous. It was finished in 123 AD, and remains the world's largest unreinforced concrete dome.
“By every measure of success from an -architectural, artistic, engineering, and age-viewpoint, the Pantheon is the greatest building that was ever built.”
The Hagia Sophia is a mosque and former church serving as a major cultural and historical site in Istanbul, Turkey. The site was an Eastern rite church from AD 360 to 1453, except from 1204-1261, when it was a Latin church. Till 1507, it was the largest Cathedral in the world. After the fall of Constantinople in 1453, it served as a mosque until 1935, when it became a museum. In 2020, the site once again became a mosque.
It was formally called the Church of God's Holy Wisdom (Greek: Holy Sophia) and upon completion became the world's largest interior space and among the first to employ a fully pendentive dome. It is considered the epitome of Byzantine architecture, because it changed the history of architecture. Interior height is 56 mtrs. Dome diameter is 33 mtrs.
One of the greatest architectural/engineering achievements of the Renaissance, Filippo Brunelleschi’s dome for Florence Cathedral was completed in 1436, and has a diameter of 45 mtrs. Built from brick, the octagonal dome remains the largest masonry dome ever built.
The construction of this Gothic masterpiece, called "Cathedral de Santa Maria del Fiore" began in 1296 and lasted for over a century. Its exterior is has white and brown paneling, and is adorned with intricate marble facades, featuring an array of sculptures and artwork.
The Dome of St. Peter's Basilica in the Vatican is Michelangelo's masterpiece, and is with 136 mtrs the tallest dome in the world. The internal diameter is 42.5 mtrs, with an opening of 8 mtrs at the top. The building itself is a cube.
Michelangelo, then in his seventies, wrote, "I undertake this only for the love of God and in honor of the Apostle." He insisted that he should be given a free hand to achieve the ultimate aim by whatever means he saw fit.
St. Peter's Basilica is one of the most renowned works of Italian Renaissance architecture, and is the largest church in the world by interior measure. However, it is neither the mother church of the Catholic Church nor the cathedral of the Diocese of Rome (held by the Archbasilica of Saint John Lateran in Rome). The basilica is cruciform in shape, with an elongated nave in the Latin cross form. Total length is 220 mtrs.
When a dome is too heavy, the sides push outward, and cracks appear throughout the bottom portion of the structure. Engineers often wrap iron rings, called tension rings, around domes. Like hoops on a barrel, the tension rings prevent the dome walls from thrusting outward. They stood the test of time.
The surface of the dome is subdivided by ribs into 16 wedge-shaped compartments with pre-ordered fields and spaces, and is entirely covered with images on a background of a golden sky of stars. Proceeding from top to bottom, we recognize the following figures: 1. The Eternal Father with outstretched hand in a gesture of blessing; 2. Seraphim; 3. Angels; 4. Cherubim; 5. Angels (some with symbols of the Passion); 6. Redeemer, Saint John the Baptist, Our Lady, Saint Paul and the Apostles; 7. Patriarchs and Bishops.
The inner dome of the lantern reaches a height of 117 metres, while the cross at the top of the dome is over 133 metres high.
Completed in 1593, the golden sphere was the final step, the crowning touch of the dome originally designed by Michelangelo and then slightly modified by architects Giacomo della Porta and Domenico Fontana. The sphere -made of 54 trapezoidal-shape pieces of mercury-gilded bronze, coated in gold- is placed on the spire of the lantern, and rises to a height of about 410 ft from the floor of the basilica and measures 8 ft in diameter. It is accessible via a narrow stairway.
By the early 1400s, Roman engineers began building two domes in one to create the illusion of even greater height. It is “double-shelled with a cavity”, then taking on an ogival shape, slenderer than the initial design.
The U.S. Capitol dome, built in 1793, gets its height from this engineering sleight of hand. The large outer dome is a thin shell, held up by a ring of curved iron ribs. Underneath it all is a smaller, self-supporting dome, visible only from the inside.
The U.S. Capitol dome is also one of the earliest domes made of pre-fabricated cast-iron ribs. The switch from heavy masonry to lightweight metal ribs in the late 18th century greatly reduced the weight of domes being built around the world.
The first US Capitol dome was finished in 1824, mimicking the Pantheon in Rome. This low dome was constructed of wood covered by copper. Light was admitted through an oculus. This created various problems. Thus, the 2nd dome drawing showed a new cast-iron dome with columns, pilasters, brackets, scores of windows and a crowning statue. The entire dome was restored again in 2017.
The dome is situated above its rotunda. It is 88 mtrs heigh and 29 mtrs in diameter. The dome is not stone, but rather cast iron carefully painted to appear to be made of the same stone as the capitol building below. It is actually two domes, one inside the other:
In the 1950s, a radical new design -- the geodesic dome -- changed the way engineers looked at domes for the first time in 2,000 years. Invented by American engineer and architect Buckminster Fuller, the geodesic dome is a partial sphere shape structured from a series of triangles, rather than a series of arches.
A new generation of oval shaped domes equipped with retractable roofs, called SkyDome, has become a popular choice for sports stadiums throughout the world.
Singapore National Stadium in Tanjong Rhu, is in 2024 the largest dome structure, measuring 310 mtrs in diameter. It opened in 2014. The Dome's roof is retractable and takes just 20 minutes to close or open it covers 95% of the seats and is made of revolutionary all-weather resistant materials. It blocks the heat from the sun and rain as well. The roof also doubles up as a giant projector screen. The lower tier seats are also retractable either mechanically or automatically, making it the only stadium capable of hosting a multitude of events like rugby, athletics, football and many others. The stadium has a sitting capacity of 55,000 people, with an innovative cooling system which is pumped from the underneath the seats consuming 15% less energy than comparable stadiums.