@Bitmoji Why? I’ll try and not use swear words. The “refresh” sucks! The old avatar made me happy, the new refreshed look is TERRIBLE. I can’t hate it more. #Fail
The unreinforced concrete dome of Rome's Pantheon - a miracle of ancient architecture that survived the fall of an empire. Nearly 2,000 years later, nobody has ever built a bigger one.
The mighty dome, built by the Emperor Hadrian between 119-128 AD, measures 142 feet in diameter - still the largest unreinforced concrete dome ever built. Its most striking feature is a 27-foot wide oculus, completely open to the elements and acting as the building's only light source.
Many believe the oculus once functioned as a giant sundial. Every year at noon on 21 April, traditionally the birthday of Rome, the sun’s rays light up the entrance - the Emperor entering the building on such occasions would have been bathed in sunlight in dramatic fashion.
Most remarkable is the secret to the structure's longevity, itself a fascinating recent discovery. Roman concrete includes calcium carbonate lumps called "lime clasts" - these were previously thought to be the result of poorly mixed concrete, but are now understood to provide "self-healing" properties. Water seeping in through cracks in the concrete has been shown to dissolve the calcium carbonate, creating a solution which then recrystallizes to plug the gaps.
It also boasts several other architectural innovations. The coffered ceiling was intended to reduce the weight of the dome (as did the oculus itself), and the mix of concrete used was exceptionally light by design. It also decreases in density moving from bottom to top, making greater use of lighter volcanic material.
The result is one of ancient Rome's best preserved monuments that will likely stand for several more millennia. It inspired countless architectural feats over the ages since, notably Brunelleschi's dome of Florence Cathedral (1436), although that was built from brick - the ancient formula for concrete being long since forgotten.
It stands today as a testament to the ancient Romans' unparalleled mastery of engineering. It even won the resounding endorsement of Michelangelo, architect of the dome of St. Peter's Basilica, for which he undoubtedly took cues from the Pantheon. Seeing it for the first time in the early 1500s, he called it "an angelic and not a human design".