At the beginning of the 15th century, the Cathedral of Santa Maria del Fiore in Florence had an embarrassing hole 45 meters in diameter at a height of more than 50 meters. For decades, architects avoided finishing it: the opening was so colossal that there were not enough trees in all of Tuscany to build a traditional wooden centering on which to support the dome while the mortar set.
In 1420, the goldsmith and architect Filippo Brunelleschi proposed a solution that most considered structural suicide: raising the structure entirely in the air, without any temporary support framework from the ground. To achieve this, he implemented an ingenious double-shell design: a thick interior dome that bears the loads and a slimmer exterior one that protects it from the weather, drastically reducing the total weight.
The real secret lay in the laying of the bricks. Brunelleschi arranged more than 4 million pieces in a diagonal pattern known as spina di pesce (herringbone). Rows of vertical bricks periodically locked the horizontal ones, preventing the courses from sliding into the abyss before the ring was closed. In addition, he integrated a series of hidden tension rings made of stone and iron chains that compressed the base like the hoops of a barrel.
The work required inventing revolutionary machinery: cranes with reversible mechanical clutches driven by oxen, capable of hoisting blocks weighing thousands of kilos without the need to unhook the animals to lower them. With an estimated weight of 37,000 tons, the structure remains today the largest masonry dome without steel reinforcement ever built.
Source: King, Ross. 'Brunelleschi's Dome: How a Renaissance Genius Reinvented Architecture'. Penguin Books, 2001.
