A Roman arch works by transferring weight outwards and downwards along its curve to two supporting points, allowing it to span wider openings than a simple lintel.
Here's a breakdown of the mechanism:
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Wedge-Shaped Stones (Voussoirs): The arch is constructed from wedge-shaped stones called voussoirs. The shape of these stones is crucial for distributing weight.
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Keystone: The keystone is the central, topmost voussoir. It's often slightly larger than the other voussoirs and is the last stone placed. Its position and shape are critical to locking the entire structure together.
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Compression, Not Tension: The arch works primarily through compression. Each voussoir presses against its neighbors. The outward thrust is contained by the abutments (the walls or supports on either side).
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Weight Distribution: The weight from above is distributed along the curve of the arch to the abutments. Each voussoir transfers the load from the one above it, down to the next, and eventually to the ground.
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Abutments: These are the supporting structures on either side of the arch. They must be strong enough to resist the outward thrust (the force pushing outwards) created by the arch. Without adequate abutments, the arch will collapse outwards.
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Temporary Support (Centering): During construction, a temporary wooden framework, called centering, supports the voussoirs until the keystone is in place and the mortar has set. Once the mortar is dry, the centering is removed.
In simple terms, the Roman arch turns downward force into outward force, redirecting the weight onto the supporting walls. This clever design allows for larger and stronger structures compared to using just vertical posts and a horizontal beam (lintel).
