Florence Cathedral

By the late thirteenth century, Florence had crushed its rival Siena and was swimming in wealth, but its cathedral was an embarrassment. Santa Reparata was small, crumbling, and entirely unsuited to a city with imperial ambitions. In 1294, the city government ordered a replacement designed to eclipse anything built by their neighbours. Arnolfo di Cambio began constructing the colossal new walls of Santa Maria del Fiore directly around the old church. Priests simply continued holding mass inside the decaying Santa Reparata while the new marble shell slowly swallowed it whole. The project outlived Arnolfo by a century. Work sputtered through the arrival of the Black Death and the passing of multiple architects until the nave finally stood complete. There was just one glaring issue left to solve. The builders had left a hole 43 metres across standing 60 metres in the air, and nobody on earth actually knew how to cover it. In 1418, the city held a competition to figure out how to vault such a massive space without the whole structure collapsing under its own weight. Mortar of the era took too long to dry, meaning bricks laid at a steep angle would simply slip and fall on the stone floor below. Filippo Brunelleschi stepped forward with an idea that sounded like madness. He proposed a double shell capable of supporting itself without any traditional wooden scaffolding. After manoeuvring his bitter rival Lorenzo Ghiberti out of the project, Brunelleschi took control. He solved the gravity problem by laying bricks in a peculiar herringbone pattern, which locked them into place as the walls curved upward. He had to invent entirely new hoisting machines just to lift the massive stone blocks into the sky, eventually sealing the vault with a heavy marble lantern. The completed cathedral soon served as the stage for the most vicious political feud of the Renaissance. During Sunday mass on 26 April 1478, assassins backed by the Pazzi family drew their blades on the ruling Medici brothers. Giuliano de Medici fell under a flurry of knives right on the cathedral floor. Lorenzo the Magnificent fought his way bleeding across the chancel and barricaded himself inside the North Sacristy. The heavy bronze doors cast by Luca della Robbia slammed shut just in time to save his life. While the political bloodstains faded, the building took on a quieter scientific life. In 1475, the astronomer Paolo dal Pozzo Toscanelli turned the masterpiece into a gigantic solar observatory. He placed a bronze plate with a tiny hole high up in the lantern. Every year on the 21st of June, a precise projection of the sun slides across the floor of the Chapel of the Cross to mark the summer solstice. Sunlight still tracks exactly over that bronze meridian line, quietly measuring the tilt of the earth onto the cold marble.