Operative Masonry on Display: Gothic Architecture, IL Duomo, and the Stonemason

Richard H. Ryder – March, 2018

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They were built to replicate heaven on earth, a way to bring bible lessons to the downtrodden, illiterate, and uneducated. In the escalating race to build ornate and impressive structures, stretching ever higher toward heaven, the laws of physics conspired to thwart construction.  But three interrelated components of the new 12th century Gothic style architecture allowed massive stone cathedrals to rise up across Europe, many of which still stand today.  In Florence Italy, a Gothic cathedral known more for its unique dome than its height is equally impressive.  These religious monuments serve as a physical testimony to the innovation and persistence of medieval architects and the skill of its builders.


Gothic architecture, first seen in France, represented modern and high-tech innovation with its roots in Romanesque architecture. The Romanesque style represented a form of architecture virtually unchanged since Roman times. It utilized the simple and limited round arch based on a circle or semi-circle and depended on large thick walls to support the ceiling’s massive weight.  As such, it only allowed for very narrow windows that limited the entry of sunlight, creating an uninspiring and dark interior.


Unmistakable 12th  century Gothic architecture introduced to France three innovations that, when combined, allowed magnificent cathedrals to rise higher than any other structure. The risk of collapse was always present, but the pointed arch, flying buttress, and vaulted ceiling were ingeniously introduced to ensure design integrity.

Gothic style was first introduced on June 11, 1144 by Abbot Sugar at the Church of Saint Denis, the burial place of French kings located on the outskirts of Paris. He called it ‘modern’, while others invoked the memory of the barbarians known as the Goths; thus, the term Gothic.  He knew the biblical story of God’s house on earth – King Solomon’s Temple. He was a visionary who realized the importance of light and the power of visibly bringing the bible to the masses through the images contained within stained glass windows. To him, light symbolized God.  By bringing in more light to the church’s interior Sugar felt he would bring them closer to their creator.  And so, he decided to rebuild the abbey church. The result was the start of a new architectural style that inspired other French towns to compete for the biggest and tallest cathedral. Soon, different expressions of Gothic architecture appeared in England, Germany, Spain, Italy, and the low countries.  By the late 1500’s, around the beginning of the Renaissance, Gothic architecture began to wane.

The Pointed Arch

Originally from the East in the first century, the pointed arch, or ogive, topping each window was a dramatic improvement over the Romanesque rounded arch and provided greater strength and flexibility. By redirecting the arch’s stress lines down instead of to the sides, walls could be built taller.  It mitigated risk of collapse and more space could be devoted to windows for interior illumination.  But, there was still tremendous lateral stress forces where the columns, or piers, on each side of the window meets the bottom of the pointed arch. As the force of this lateral movement increased, cracks and fissures formed above the arch and lateral pressure transferred to the larger columns supporting the ceiling.  As the lateral movement at the bottom of the large columns pushed outward, the tops of these columns moved laterally inward forming an hourglass shape.  This multidirectional movement can result in total collapse.  It was the ingenious flying buttress, like those at Notre Dame Cathedral in Paris, that counteracted the pressure.

Flying Buttress   

The flying buttress, outside the structure, applies lateral inward pressure on the bottom stone of the pointed arch above each window, and it must be placed precisely to be effective. By preventing outward lateral movement, cracks and fissures above the arch are avoided, and the integrity of all columns is preserved.

The Vaulted Ceiling   

The vaulted ceiling leverages the pointed arch design to safely and effectively distribute vertical weight to the large connected supporting columns. Basically, it is two pointed arches that intersect at right angles to each other.  Like the pointed arch over a window that distributes weight downward, so do each of the two intersecting pointed arches in the vaulted ceiling.  When combined with the pointed arched windows and flying buttresses, an architectural skeleton distributes weight downward throughout the columns instead of the walls.  The vaulted ceiling allows less columns, and those that do exist are taller and thinner. This combination of three innovative architectural components allows the expansive and tall cathedrals we see throughout Europe.  They allow a large-scale interior, fully illuminated with sunlight, light that has passed through beautiful stain glass windows depicting narratives from the bible and consuming the external walls.


In some respects, the stained-glass windows found in Gothic Cathedrals is the message; the structure is just the container. Image the awe-struck people, uneducated and illiterate, viewing the narrative of the bible represented in stained glass, brightly lit by natural light, especially the iconic and large round rose window, usually above the west door. For many, it was their first opportunity to see and absorb the message of God.  Sounds of musical instruments and angelic voices echoed through an expansive structure shaped like a crucifix.  The size and scale of the cathedral and the intense stimulation of their senses must have been humbling, overwhelming, and powerful.

The process of creating stained glass has basically gone unchanged through the ages. In the 12th century pulverized quartz crystals were combined with soda ash (burnt vegetable matter) and various metals for color.  Copper produced green and red, cobalt produced blue, and selenium produced orange and yellow. Medieval designers had to be both craftsmen and chemist.


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If you travel to Florence, Italy you can’t miss the Basilica di Santa Maria del Fiori – “Our Lady of the Flower”, a splendid example of Italian Gothic style architecture, which some say was a break from traditional Gothic style. What makes this cathedral distinctive is the freestanding dome that towers over the city.  Referred to as “IL Duomo” it is synonymous with the church itself. The innovation required to construct the dome was unprecedented and serves as a backdrop for the life of an operative stonemason.

Cathedral construction began in 1296, but by 1418 a large hole existed in the roof of the uncompleted structure where a dome was planned.  Unanswered was how to build the dome 150 feet across with a base 180 feet above ground. Unlike those in France, this cathedral had no flying buttresses or pointed arches; but, unlike in France, architects were trying to solve another perplexing problem – how to erect a massive, freestanding dome on an octagonal floor, 35 feet across. To find an architect able to solve the mystery a contest was created with a prize of 200 gold florins (about $28,000, today).

Many creative designs were proposed, but Filippo Brunelleschi, a stubborn and hot-tempered goldsmith, proposed one dome nested inside the other, which made the structure lighter and loftier. According to Tom Mueller, in the February 2014 issue of National Geographic, “he had mastered drawing and painting, wood carving, sculpture in silver and bronze, stone setting, niello, and enamel work. Later he studied optics and tinkered endlessly with wheels, gears, weights, and motion, building a number of ingenious clocks, including what may have been one of the first alarm clocks in history. Applying his theoretical and mechanical knowledge to observation of the natural world, he single-handedly worked out the rules of linear perspective. He’d just spent several years in Rome measuring and sketching the ancient monuments and noting, in cipher, their architectural secrets. Indeed, Brunelleschi’s life seemed to have been one long apprenticeship for building the dome of unequaled beauty, usefulness, honor, and power that Florence yearned for.”

Brunelleschi faced many design issues. One significant obstacle was hoop stress in the unusual octangular and pointed cupola; that is, outward pressure caused by excessive weight.  His solution leveraged horizontal stone, iron, and wood rings to relieve tension, similar to a hoop barrel. A second challenge was how to lift heavy material during dome construction.  Mueller tells us that “Brunelleschi the clockmaker and tinkerer outdid himself. He invented a three-speed hoist with an intricate system of gears, pulleys, screws, and driveshafts, powered by a single yoke of oxen turning a wooden tiller. It used special rope 600 feet long and weighing over a thousand pounds and featured a groundbreaking clutch system that could reverse direction without having to turn the oxen around.”

Stonemasons and the Little People

Construction of the dome began in 1420. Over the course of the next 16 years most day to day construction fell upon the popola minuto – the “little people”, who were over 300 unskilled building trade workers from poor families. They worked not only on the dome carrying lime and bricks, but also in local quarries, where men could earn their apprenticeship as masons. In doing so they learned not only how to identify the best stones, but how to cut and dress them per the architect’s templates drawn on parchment or carved in wood.

The stone masons were woken each morning by church bells and, carrying their lunch in leather pouches and their own tools, they reported for work. Those assigned to the dome reached their work site by ascending several hundred steps with sandstone threads. Using personal chisels, T squares, hammers, trowels, and mallets they worked all day; their time at work measured by hourglass. Unable to leave the dome for lunch, they consumed it several hundred feet above the ground. Carrying their own flasks, workers drank wine in moderation to quench their thirst; not only did it have medicinal value, but it lacked the bacteria commonly found in water. They worked dawn to dusk, Monday through Saturday; their only rest occurred on the Sabbath and during religious feasts.  Even after a strike, the workers failed to make their life better.  After relenting to pressure they returned to work with a forced reduction in pay.

The grueling work did not come without great risk, since injury or death had personal and financial consequences.  There was danger lurking everywhere; even nesting pigeons in the dome caused concern. To prevent falls a leather safety harness was worn and board parapets suspended from scaffolds blocked the view of nervous workers.  When accidents did occur, there was little help available to the victim and his family, especially in death, of which only three occurred.  As supportive as the Mason Guilds were, they did not assist the disabled or widows and orphans. Their only obligation to a dead worker was to attend his funeral.  The Guild of Stonemasons and Carpenters was more focused on benefiting the elite than the worker.

Tools and Techniques

In addition to the personal tools owned by each mason, other instruments were employed. Levels shaped like the letter “A” ensured laid stones were perpendicular.  Plumb lines, made of string and a lead weight, hung from the level’s apex checked horizontals. Structured curves of individual building components were first plotted in full-scale, blueprint style, and laid out on special tracing floors that were later covered in plaster of Paris.  These life-size geometrical designs were used to create wooden templates for the quarry masons to form a sandstone piece.

Ross King in his book, Brunelleschi’s Dome, explains that stones were cut by hand from a hillside, removed using a crowbar and wooden wedge, cut to size with a pickax, and dressed by hammer with a light blade.  To test the quality of the stone it was struck with a light hammer.  If it rang like a bell, there were no flaws; a dull sound indicated a crack or other flaw and thus discarded.  Another test was to smell the freshly removed stone from the quarry.  Limestone and sandstone smelled like rotten eggs and the stronger the sulfurous smell, the better the quality.   

Shells, Bricks, Arches, and Rings

From the ground, the people of Florence watched as the dome took shape, lighter and loftier than solid domes found elsewhere. To this day, four major components work in tandem to give IL Duomo its distinctive, half egg look: Shells, Bricks, Arches, and Rings.

The dome utilizes two concentric shells that were constructed simultaneously with the inner shell six feet thick and a taller, thinner outer shell one third the size.  The shells were constructed with brick, which is lighter than stone and easier to form.  To ensure quality, the basic 10” x 5” inch brick, known as the mattone, was first checked on site by inspectors of the Masons Guild, recognized by their blue capes and silver badges. The seasoning and burning process of bricks took up to two years, so proper planning was critical. Mortar made of lime, sand, and water was mixed on the cupola to allow application while it was still plastic, followed by a two-step setting process    A variety of designs were used to accommodate an octagonal pattern, including rectangular, triangular, dovetailed, and flanged. The unique construction called for many different sizes and shapes, and bricks were laid horizontally for three or four feet, then interrupted by vertical bricks.  In addition to allowing the mortar to better cure, this herringbone pattern, critical to the dome’s structure, allowed the vertical bricks to lock in the horizontal bricks. The sideways pressure of this brick pattern counterbalanced inward gravity.

Another key architectural component of the dome was the “quinto acuto” arch or pointed fifth curvature.  Visualize the Mastercard logo and the overlapping circles.  If you cut the overlapped area in half, horizontally, the upper half forms a quinto acuto shape.  It not only was aesthetic to the eye, but it was a structural necessity.  Gothic architecture made liberal use of the pointed arch and Ross King tells us “it has two distinct advantages over the rounded or semicircular arch.” He explains that the first has to do with proportions, for it can rise higher over an equivalent span; almost a third higher.  Secondly, due to its height it can reduce radial thrust. This approach allows the stones to remain in place by mutual pressure from their own weight.

But quinto acuto was not the sole reason that allowed the dome to be self-supporting and thus not implode under its own weight.  Within the dome a skeleton of nine horizontal circular rings strengthened the inside of the outer shell.  Installed every eight feet these 3-foot-wide and two-foot-high chestnut beams, in harmony with the double shell, brick patterns, and arches resulted in an architecturally beautiful work of art that has withstood the test of time for almost 600 years.

On March 25, 1436, after 140 years of construction a Feast of the Annunciation, marked by the tolling of bells, was held to consecrate the magnificent structure. According to Ross King “The height and span of the dome has never been surpassed”.  King also explains that St. Peter’s dome at the Vatican is almost 10 feet narrower; St. Paul’s in London is 30 feet smaller; and the Capitol in Washington D.C. is less than two thirds the size.

Considering that IL Duomo was built using primitive tools by today’s standards, its innovative construction continues to serve as an architectural marvel and a testimony to the skill of its workers.

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