Why are wedge-shaped bricks useful in building arches?

Wedge-shaped blocks, known as voussoirs, are essential to arch construction because they allow the structure to support heavy loads through compression.12

When these blocks are set flank to flank, downward pressure does not push them apart; instead, it forces the voussoirs tightly together. This mechanism enables the arch to span wider openings using smaller, manageable pieces of brick or stone rather than massive, monolithic beams. The central wedge-shaped block, called the keystone, is particularly critical as it locks the other pieces in place, completing the arch and allowing it to become self-supporting.123

Because these forces also create a diagonal outward pressure known as thrust, the arch must be properly supported by massive vertical structures or buttresses to prevent collapse.12