In the wake of COP21 I've been reminded of the value of taking decisions that we may never fully appreciate the benefits of.

The story of Florence's Cathedral has that in spades.

On 9th September, 1296 the first stone was laid for Florence's landmark cathedral, The Basillica di Santa Maria del Flore, or "Duomo". Designed by Arnolfo di Cambio, the following 120 years would see around 10 different architects oversee its construction, as section by section they pieced together Cambio's monumental jigsaw. The basic features of the dome had been set at the start; Cambio's brick model calling for an octagonal dome higher and wider than any that had ever been built.

But it wasn't until 1367 that Neri di Fioravante settled the shape of the dome as one with no external buttresses. His model was one of the first events of the Italian Renaissance and a grand rejection of the Gothic, buttressed preferences favoured by their enemies in the North. However, the Florentines did not have the technology to build such a dome since it required an internal anti-spreading system that had not yet been designed and there was not enough timber in Tuscany to build the scaffolding and forms. So when it was conceived, and when the shape was finally settled in 1367 by Neri, the dome posed both technical and cultural problems.

This did not deter the Florentines. They continued building and each year the master craftsmen swore an oath to complete the dome in accordance with Neri's 1367 design. By 1418, 122 years after construction started, only the dome remained incomplete.

In August of 1418, Filippo Brunelleschi, supported by Cosimo de Medici, received the commission to design the dome's structure without revealing the complete plans (to retain control). It was bold to say the least: knowledge of the physical laws needed to understand the engineering, and the tools for calculating stress, were centuries away. All Brunelleschi had to rely on was intuition and whatever he could learn from the large scale models he built.

The Cathedral, begun in 1296, saw it's complete structure finally finished 173 years later in 1469. But the facade was still unfinished and would remain so until the 19th century. The dome is still the largest masonry dome in the world.

The courage and determination of the Italians to persevere with a vision (that had been so successfully cast it had become sacrosanct in the process) is an extraordinary example of how sometimes it's necessary just to start with a dream, an incomplete plan and a strategy that consists merely to be guided by faith, principle and patience. And, finally, a willingness to persevere in the knowledge that not only may we have no idea how to complete the task, but that it may fall to others a long way down the line to enjoy the final fruits of our labour.