Have you tried building a house using Lego blocks? What if you built a huge room, and want to put a flat roof on it? You’d probably add some walls or pillars to support it. These vertical supports take the roof’s load and transfer it to the ground. Many buildings are built with vertical columns and horizontal beams or lintels to distribute the load. Many ancient buildings use this system of post and lintel construction.
Early builders were constantly innovating to create bigger buildings to impress their friends and enemies. The Romans, famous for their architectural skills, managed to build massive rooms uninterrupted by walls and pillars. How did they do this? Enter, arches and domes.
Arches were used by many early civilisations, but the Romans perfected it. They were also the first to use concrete extensively and developed mastery over it. Concrete can be moulded in any shape and used to create curved roofs like domes. The dome blurred the lines between the roof and the wall, and could create huge rooms without any intermediate supports.
With arches, domes and concrete, some of the most impressive architectural structures were born. One such is the Pantheon, a Roman temple with a soaring concrete dome that would put modern structures to shame. Built in around 125 CE, its dome remains the largest ‘unreinforced’ dome in the world; i.e. it has no steel rods that help hold the concrete together.
A cross-section of the Pantheon showing how a sphere with a diameter of 43.3m fits under its dome. | Photo Credit: Wikimedia Commons
Picture eight to 10 giraffes standing one above the other. That’s how high the topmost part of the dome is. The dome itself has a radius of 71 feet and the entire building is 142 feet wide and 142 feet tall. What do you think these numbers mean? Its geometry was such that you can fit a massive perfect sphere inside the Pantheon.
The walls are made of brick and concrete and a series of arches hidden inside the walls provide extra support. The concrete was extra-special and ultra-strong, and has kept the building standing for almost 2000 years.
The occulus: the single opening at the top | Photo Credit: Flickr
You know now that the Pantheon is gigantic. Guess how many doors and windows it has? Just one each! Its only source of light is a 30 ft opening — an oculus — at the centre of the dome. This has another important purpose: it is integral to keep the structure standing.
If you visit Rome when it’s raining, visit the Pantheon and watch a sheet of water fall right into this beautiful building.
Arch explained
In an arch, each brick transfers the load to the next one, and finally to the wall and floor. The arch’s most important part is the central stone or ‘key stone’. An arch can allow for much wider spans than flat roofs.
