The Dome of Florence Cathedral.
In 1419 Filippo was given the task of completing the dome for the Cathedral of Florence. This work occupied a great deal of Brunelleschi's life and the challenge was enormous, no dome of that size had been built since antiquity.
The dome became not only an architectural problem, but also demanded great engineering skill and Filippo invented, and patented, a new hoisting machine for raising the masonry required for the dome. Work began in 1420 and was completed in 1436.
The dome contains over 4 million bricks and the structure rests on a drum, not on the roof itself, this allowed the dome to be built without the need for scaffolding from the ground. The two shells of the dome are supported by ribbed reinforcements and are joined by horizontal and vertical struts through which the staircase weaves it's way to the top of the structure.
The base of the dome is tensioned by horizontal chains of iron and wood. (The elders of Florence had forbidden the use of external buttresses, and this was a part of the architect's solution to the problem).
The cathedral dome still dominates the skyline of Florence today, it remains as a lasting testament to a great architect.
Visit if you can Florence is a magnificent city. If you look at the cupola (bellow) it's just possible to see the visitors at the top of the dome this gives some idea of the huge scale of the building.