![\"pantheon\"](\"https:\/\/i1.wp.com\/sarahgildea.com\/blog\/wp-content\/uploads\/2019\/02\/PantheonFeatured-Blog-1.jpg?ssl=1\")
<\/a>\n<\/div>\nMany architects have written their masters thesis on it, giving their account of how they believe it was built. Unfortunately, the architect of this present building didn\u2019t leave us the blueprint, and that was probably done on purpose. The Pantheon is architectural showing-off. It was built for wonder and prestige. Michelangelo had said that it \u201ccouldn\u2019t have been made by human hands \u2013 it had to have been made by angelic hands\u201d.<\/p>\n
What I want to draw upon today is the uncommon features of the Pantheon \u2013 the things little discussed, the questions that are hard to get answers to \u2013 I am referring to the construction of the roof\/ceiling.<\/p>\n
It was created with Roman mortar poured into a wooden frame. However, the roof is 19 feet (5.69 meters) thick at the base, working its way up to 5 feet (1.5 meters) thick at the top. That\u2019s a lot of mortar. And, there is no metal support in the roof.<\/p>\n
<\/p>\n
Part I \u2013 A Lesson in Mortar<\/strong><\/h2>\n\u00a0Thanks to: Lynne C. Lancaster,\u00a0Concrete Vaulted Construction in Imperial Rome.<\/em><\/p>\n\u00a0 \u00a0 \u00a0Roman mortar is stronger than any other type of mortar because they added\u00a0pozzolana<\/em>, a volcanic ash, which creates a chemical reaction that is much stronger than lime. It gets hard when mixed with water, so it can also set underwater.\u00a0By comparison, a simple lime mortar is made of quartz sand, slaked lime\u00a0and water, and hardens and gains strength through contact with\u00a0air\u00a0\u2013 or better \u2013 carbon dioxide. Therefore, the mortar in the centre of the mass made with simple lime mortar is not as strong as the stuff outside.<\/p>\nPozzolana<\/em>\u00a0(the ash of limestone) contains both silicon dioxide and\u00a0alumina<\/strong>\u00a0(alluminum dioxide), and has a chemical reaction to the water and slaked lime. Discovered by Romans by the bay of Naples in 2nd century BC, they called it\u00a0pulvis puteolanus<\/em>\u00a0(Puteoli<\/em>\u00a0= \u2018to stink\u2019, because of the sulfur smell. Modern Pozzuoli).\u00a0Modern cements lack the alumina, and this is why it degrades after about 50 years. Roman mortar is still around and fighting 2,000 years after it was put in place.\u00a0<\/p>\nMortar made with pozzolan acquires greater strength when it is cured with water, and is 5 to 8 times stronger than anything we have today.\u00a0The Church of St. Sebastian on via Appia Antica marks the location of the quarry for the red pozzolan.\u00a0This is the ‘dirt’ that the Christians were digging into to create the catacombs. It is a high quality pozzolan. Black pozzolan was used by Trajan and Hadrian (Pantheon), and was of even higher quality.P<\/em><\/p>\nCocciopesto<\/em>\u00a0is a mortar made with crushed terracotta, and often also contains pozzolan. It is also suggested for use because it\u2019s also very strong \u2013 and water resistant.\u00a0Cocciopesto was used from the 2nd century BC mainly to line cisterns and to protect the extrados of vaults exposed to the elements.\u00a0This was used in the Pantheon, and would serve to divert water even if the vault developed cracks.<\/p>\n <\/p>\n
Part II \u2013\u00a0<\/strong>Some Lessons in Ancient Engineering<\/strong><\/h2>\nThe Water Screw<\/strong><\/h3>\n![\"Water](\"https:\/\/i2.wp.com\/sarahgildea.com\/blog\/wp-content\/uploads\/2019\/02\/Archimedes_screw-Blog.jpg?resize=150%2C146&ssl=1\")
<\/figure>\nIn the 3rd century BC, there was a very important scientist\/ mathematician named\u00a0Archimedes<\/strong>. He was called \u2018the wise one\u2019, \u2018the master\u2019 and \u2018the great geometer\u2019. Among other things, he invented integral calculus, systemised the use of leverage to lift objects that would have been impossible otherwise, and he invented the \u201cwater screw\u201d. Cicero restored his tomb more than a century after his death, which tells us that Archimedes was still a huge hit, and studied by all budding architects, scientists and mathematicians after him.<\/p>\n![\"Model](\"https:\/\/i0.wp.com\/sarahgildea.com\/blog\/wp-content\/uploads\/2019\/02\/TrajanColumn-Blog.jpg?resize=117%2C150&ssl=1\")
<\/a><\/p>\n\u00a0Apollodorus of Damascus<\/strong>\u00a0was the full time architect for the emperor Trajan (98-117). Hadrian was a soldier who worked his way through the Roman ranks and became a trusted confident of Trajan. They all knew each other very well. Hadrian became emperor after Trajan (117-138).\u00a0\u00a0 \u00a0 Apollodorus studied the works of Archimedes, and like Archimedes, was asked to create war machines and other weapons for military warfare. Apollodorus possibly saw inspiration in the water screw as a means of creating a new propaganda piece \u2013 Trajans\u2019 Column.<\/p>\n![\"Diagram](\"https:\/\/i0.wp.com\/sarahgildea.com\/blog\/wp-content\/uploads\/2019\/02\/PantheonSpiral2-Blog.jpg?resize=148%2C99&ssl=1\")
<\/a><\/p>\n\u00a0 \u00a0 Could Hadrian have used something similar in the wooden frame necessary to create the Pantheon dome?\u00a0\u00a0 \u00a0 It certainly would have been handy to bring tools and workmen up to the frame area, and it had been done before \u2013 in the military.\u00a0\u00a0 \u00a0 However, the dome was twice the size of any dome that had been created before.\u00a0\u00a0 \u00a0 The overall design of the Pantheon is modelled on a sphere within a cylinder, which is the device that Archimedes had carved on his tomb as representing one of his great mathematical discoveries \u2013 his theory determining the 2:3 relationship between the volume of a sphere and a cylinder.<\/p>\n
\u00a0 \u00a0 \u00a0According to this diagram, the Pantheon dome starts exactly at the 1\/2 way point of the structure \u2013 at the 21.6 meters from the ground. BUT \u2013 it doesn\u2019t become independent of the walls until 1\/3 of the way into the dome. Only 2:3 of the dome is actually independent and \u2018floating\u2019 \u2013 in need of support.<\/p>\n
\u00a0*The two diagrams above, courtesy of\u00a0Lynne C. Lancaster,\u00a0Concrete Vaulted Construction in Imperial Rome.<\/em><\/p>\n <\/p>\n
Part III \u2013 The Dome\u00a0of\u00a0the\u00a0Pantheon<\/strong><\/h2>\n![\"Pantheon](\"https:\/\/i1.wp.com\/sarahgildea.com\/blog\/wp-content\/uploads\/2019\/02\/PantheonTop-Blog.jpg?resize=150%2C106&ssl=1\")
<\/a><\/p>\nThe\u00a0 pozzolan was mixed with successively less dense aggregate stones, such as pieces of pumice in the higher layers. Authors Mark and Hutchison estimated that, if normal weight concrete had been used throughout, the stresses in the arch would have been some 80% greater.\u00a0Now, the entire dome wasn\u2019t caste at the same time \u2013 the change in stone mixture demonstrates this, plus there are 7 step-rings on the outside, where the dome becomes independent from the base structure \u2013 6 with brick facing, with diameters decreasing towards the ascent.<\/p>\n
![\"Photo](\"https:\/\/i0.wp.com\/sarahgildea.com\/blog\/wp-content\/uploads\/2019\/02\/PantheonRepair-Blog.jpg?resize=112%2C150&ssl=1\")
<\/a><\/p>\nThe use of coffers in the Pantheon complicated the construction. The coffers had to be independent from the centering\u00a0structure. The centering, formwork and coffers comprised such a complex network that the centering frames were likely constructed so that they could be disassembled and removed in parts. By the way, they are commonly referred to as \u201csquare\u201d coffers, but they are not \u2013 they are trapezoid shaped. The largest ones are estimated to be 12.75 feet (3.88m) wide, and the smallest ones are 8 1\/2 feet (2.62m) wide. The smooth surface above them is estimated at 28 feet (8.5m) wide.\u00a0Because of the angles of the coffer boxes, they would have been removed individually, because the edges of the boxes are all at different angles, so could not have slid straight down.<\/p>\n
![\"Diagram](\"https:\/\/i1.wp.com\/sarahgildea.com\/blog\/wp-content\/uploads\/2019\/02\/Pantheon_section_sphere-Blog.jpg?resize=150%2C109&ssl=1\")
<\/a><\/p>\n28 coffers in 5 rows is another problem: The simple order of the ceiling coffers would be a 16 point geometry \u2013 divide the circle in halves, quarters, eights, then 16ths. Dividing the ceiling into 28 parts is not possible with a simple straight edge and pencil.\u00a0We don\u2019t (officially) know the symbolism behind the 28 and 5 rows, but we know Hadrian loved\u00a0symbolism (just like St. Augustine). It could be a reference to the approximate number of days in a month in the lunar calendar. The ancient Romans had used the unreliable lunar calendar until Julius Caesar changed it. However, we are now in the 2nd century AD … I have my own theory of the symbolism in the ceiling, because the architect used a similar symbol on the floor!<\/p>\n
\u00a0 \u00a0 \u00a0Roman mortar is stronger than any other type of mortar because they added\u00a0pozzolana<\/em>, a volcanic ash, which creates a chemical reaction that is much stronger than lime. It gets hard when mixed with water, so it can also set underwater.\u00a0By comparison, a simple lime mortar is made of quartz sand, slaked lime\u00a0and water, and hardens and gains strength through contact with\u00a0air\u00a0\u2013 or better \u2013 carbon dioxide. Therefore, the mortar in the centre of the mass made with simple lime mortar is not as strong as the stuff outside.<\/p>\n Pozzolana<\/em>\u00a0(the ash of limestone) contains both silicon dioxide and\u00a0alumina<\/strong>\u00a0(alluminum dioxide), and has a chemical reaction to the water and slaked lime. Discovered by Romans by the bay of Naples in 2nd century BC, they called it\u00a0pulvis puteolanus<\/em>\u00a0(Puteoli<\/em>\u00a0= \u2018to stink\u2019, because of the sulfur smell. Modern Pozzuoli).\u00a0Modern cements lack the alumina, and this is why it degrades after about 50 years. Roman mortar is still around and fighting 2,000 years after it was put in place.\u00a0<\/p>\n Mortar made with pozzolan acquires greater strength when it is cured with water, and is 5 to 8 times stronger than anything we have today.\u00a0The Church of St. Sebastian on via Appia Antica marks the location of the quarry for the red pozzolan.\u00a0This is the ‘dirt’ that the Christians were digging into to create the catacombs. It is a high quality pozzolan. Black pozzolan was used by Trajan and Hadrian (Pantheon), and was of even higher quality.P<\/em><\/p>\n Cocciopesto<\/em>\u00a0is a mortar made with crushed terracotta, and often also contains pozzolan. It is also suggested for use because it\u2019s also very strong \u2013 and water resistant.\u00a0Cocciopesto was used from the 2nd century BC mainly to line cisterns and to protect the extrados of vaults exposed to the elements.\u00a0This was used in the Pantheon, and would serve to divert water even if the vault developed cracks.<\/p>\n <\/p>\n In the 3rd century BC, there was a very important scientist\/ mathematician named\u00a0Archimedes<\/strong>. He was called \u2018the wise one\u2019, \u2018the master\u2019 and \u2018the great geometer\u2019. Among other things, he invented integral calculus, systemised the use of leverage to lift objects that would have been impossible otherwise, and he invented the \u201cwater screw\u201d. Cicero restored his tomb more than a century after his death, which tells us that Archimedes was still a huge hit, and studied by all budding architects, scientists and mathematicians after him.<\/p>\n \u00a0Apollodorus of Damascus<\/strong>\u00a0was the full time architect for the emperor Trajan (98-117). Hadrian was a soldier who worked his way through the Roman ranks and became a trusted confident of Trajan. They all knew each other very well. Hadrian became emperor after Trajan (117-138).\u00a0\u00a0 \u00a0 Apollodorus studied the works of Archimedes, and like Archimedes, was asked to create war machines and other weapons for military warfare. Apollodorus possibly saw inspiration in the water screw as a means of creating a new propaganda piece \u2013 Trajans\u2019 Column.<\/p>\n \u00a0 \u00a0 Could Hadrian have used something similar in the wooden frame necessary to create the Pantheon dome?\u00a0\u00a0 \u00a0 It certainly would have been handy to bring tools and workmen up to the frame area, and it had been done before \u2013 in the military.\u00a0\u00a0 \u00a0 However, the dome was twice the size of any dome that had been created before.\u00a0\u00a0 \u00a0 The overall design of the Pantheon is modelled on a sphere within a cylinder, which is the device that Archimedes had carved on his tomb as representing one of his great mathematical discoveries \u2013 his theory determining the 2:3 relationship between the volume of a sphere and a cylinder.<\/p>\n \u00a0 \u00a0 \u00a0According to this diagram, the Pantheon dome starts exactly at the 1\/2 way point of the structure \u2013 at the 21.6 meters from the ground. BUT \u2013 it doesn\u2019t become independent of the walls until 1\/3 of the way into the dome. Only 2:3 of the dome is actually independent and \u2018floating\u2019 \u2013 in need of support.<\/p>\n \u00a0*The two diagrams above, courtesy of\u00a0Lynne C. Lancaster,\u00a0Concrete Vaulted Construction in Imperial Rome.<\/em><\/p>\n <\/p>\n The\u00a0 pozzolan was mixed with successively less dense aggregate stones, such as pieces of pumice in the higher layers. Authors Mark and Hutchison estimated that, if normal weight concrete had been used throughout, the stresses in the arch would have been some 80% greater.\u00a0Now, the entire dome wasn\u2019t caste at the same time \u2013 the change in stone mixture demonstrates this, plus there are 7 step-rings on the outside, where the dome becomes independent from the base structure \u2013 6 with brick facing, with diameters decreasing towards the ascent.<\/p>\n The use of coffers in the Pantheon complicated the construction. The coffers had to be independent from the centering\u00a0structure. The centering, formwork and coffers comprised such a complex network that the centering frames were likely constructed so that they could be disassembled and removed in parts. By the way, they are commonly referred to as \u201csquare\u201d coffers, but they are not \u2013 they are trapezoid shaped. The largest ones are estimated to be 12.75 feet (3.88m) wide, and the smallest ones are 8 1\/2 feet (2.62m) wide. The smooth surface above them is estimated at 28 feet (8.5m) wide.\u00a0Because of the angles of the coffer boxes, they would have been removed individually, because the edges of the boxes are all at different angles, so could not have slid straight down.<\/p>\n 28 coffers in 5 rows is another problem: The simple order of the ceiling coffers would be a 16 point geometry \u2013 divide the circle in halves, quarters, eights, then 16ths. Dividing the ceiling into 28 parts is not possible with a simple straight edge and pencil.\u00a0We don\u2019t (officially) know the symbolism behind the 28 and 5 rows, but we know Hadrian loved\u00a0symbolism (just like St. Augustine). It could be a reference to the approximate number of days in a month in the lunar calendar. The ancient Romans had used the unreliable lunar calendar until Julius Caesar changed it. However, we are now in the 2nd century AD … I have my own theory of the symbolism in the ceiling, because the architect used a similar symbol on the floor!<\/p>\nPart II \u2013\u00a0<\/strong>Some Lessons in Ancient Engineering<\/strong><\/h2>\n
The Water Screw<\/strong><\/h3>\n
<\/figure>\n<\/a><\/p>\n<\/a><\/p>\nPart III \u2013 The Dome\u00a0of\u00a0the\u00a0Pantheon<\/strong><\/h2>\n
<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n