When the Florence Cathedral was constructed, architects designed a massive octagonal opening for its dome, but for nearly a century no one knew how to build it. The span was too wide for conventional wooden scaffolding, as the required timber was unavailable and the structure would collapse under its own weight during construction. Goldsmith turned architect Filippo Brunelleschi proposed a radical structural solution that relied entirely on geometry and physics.
He designed a double-shell octagonal dome with an outer wall protecting an inner structural shell. To prevent the bricks from falling inward while laying them, Brunelleschi invented a herringbone brickwork pattern called spina di pesce. In this arrangement, vertical bricks acted as anchors, locking the horizontal bricks into place as each ring was completed.
Additionally, he incorporated concealed horizontal chains made of oak timber and iron rings embedded within the brickwork to resist the lateral tension forces pushing outward. Without relying on flying buttresses or heavy wooden centering, Brunelleschi created a self-supporting masonry dome weighing over 37,000 metric tons, which remains the largest unsupported masonry dome ever built.