Why did Roman arches allow builders to span wider spaces than stone slabs could span?

Roman arches allowed builders to span wider spaces than traditional stone slabs—known as lintels—primarily due to their geometry and the way they manage structural stress.12

In a post-and-lintel system, a horizontal stone slab is limited by its own weight and its inherent weakness in tensile strength, which makes it prone to breaking if the span is too wide. By contrast, an arch is a curved structure that functions by converting downward pressure into compressive force.314

Key advantages of the arch include:
* Material Efficiency: Arches can be constructed using smaller, manageable voussoirs (wedge-shaped blocks) rather than massive, monolithic stone slabs, which are difficult to transport and install.12
* Load Distribution: The curved shape forces the blocks together under pressure, effectively conducting loads downward into the supports rather than bending the material downward as a lintel would.24
* Structural Stability: When properly buttressed, the arch can support significantly greater loads, and when placed in a row, the thrust of one arch can counteract the thrust of its neighbors.12