12/06/2026
You don't have to work in the built environment to appreciate the beauty, craftsmanship and engineering behind St Paul's Cathedral.
My wife often rolls her eyes when we're out and about and I start pointing out building defects, discussing interesting design features, or trying to figure out what construction work is taking place. On our recent trip to London, though, it was great to simply stand back and admire this incredible building together.
As an added bonus, a wedding was taking place during our visit. The singing and acoustics were truly spectacular.
St Paul's Cathedral was completed in 1710, which makes the scale of the engineering and construction achievement even more remarkable.
One detail I had never appreciated before is that the famous dome dominating the London skyline is actually a "triple dome" design.
The outer dome that everyone sees is supported by a concealed middle brick cone. A third, inner dome sits beneath it, serving a decorative purpose. It hides the structural cone from view while providing a canvas for the ornate paintings and murals inside.
After doing some further reading, I discovered this fascinating detail about the middle brick cone:
"Hidden completely from sight between the inner and outer layers is a massive, 18-inch-thick brick cone. This is the actual powerhouse of the structure. Christopher Wren [who designed St. Paul’s] used the equation of an inverted catenary arch (the natural shape a hanging chain makes under its own weight), which is mathematically the most stable shape for supporting downward load. This hidden cone bears the crushing weight of the 850-tonne stone lantern at the very top."
It's an incredible example of engineering ingenuity hidden in plain sight.
Throughout the cathedral there are numerous arches, domes and circular structural details present. They not only play a critical role in supporting the building, but also create beautiful architectural lines.
So what makes arches so strong?
Arches are used in construction because they efficiently span wide openings while supporting massive loads. Their curved shape directs gravity and other loads outward and downward into the supporting structures, converting all vertical pressure into compression force.
This is important because materials such as stone, brick and concrete perform exceptionally well under compression but are much weaker under tension. The geometry of an arch allows these materials to support enormous loads without bending or cracking.
What struck me most during the visit was how seamlessly engineering and architecture come together. Features such as arches and domes aren't just visually impressive, they are fundamental to the structural integrity of the building.
