Although many people assume that stained glass was developed to fill in the huge windows that came with Gothic architecture, we have seen that windows were coloured and decorated in various ways long before the Gothic, and were used to create a sense of divine presence inside the church.

Think about that. God is, by Medieval definition (Anselm, Archbishop of Canterbury, 1093-1109) the most powerful thing you can think of. So what effect would He have on a building?

• Would it collapse as if hit by an earthquake?
• Or would it burst apart at the seams?
• Or would it be able to defy gravity, floating serenely on his perfection?
• Or would it come to life and grow like a forest?
• Or would it vibrate like a turbine engine?

All these ideas and more are reflected in Gothic architecture (c.1140 onwards). But to appreciate them best, you need to get just a little technical. After that it's a breeze.

Explanation and a few terms

Remember, a Gothic building holds itself up very well—check out the Medieval Search for the Perfect Vault, if you've forgotten. So these ideas about God had to be represented in the decoration. The decoration is all illusion, but it looks structural.

The decoration looks structural because it takes the form of high-relief ribs. Whether we know it or not, most of us visualize structure as if it followed the rules of building in wood (our earliest building material, ever). Under those rules, the ribs would be structural because they would be holding up the vault, like joists and rafters hold up ceilings.

But vaults are made of stone, and stone follows different rules. Stone must push against itself, or it will crack apart. That is why the vault must be curved, to make the stones push against each other. Thus, once built, every part of a stone vault supports itself. The ribs are pure decoration.

Remember that, because it goes against everything you want to believe, and everything most "experts" and publications will try to tell you. And that's the point. In the Gothic period, artists and thinkers were investigating the difference between appearance and reality in unprecedented depth, and they really exploited the misleading appearance of vaults!

Why? Because churches are God's house. If you missed them earlier, these links will explain how churches were designed to be Classically Beautiful (i.e. by scientific rule) in structure (vaults) and colour (windows) so that they could manifest Him. But God is invisible. So, how better to represent Him than to use the insubstantial unreality of appearance to suggest that the physical church can hardly contain Him!

You may have been taught that there are several different kinds of vault with impossible names. This is only true in a visual sense. There is only one structure: the domed-up groin vault, with or without ribs. Diagram 1 shows you the structure and names the useful parts. You want to know what a tierceron vault is, too. Diagram 2 shows you that, and then labels the tiercerons (the decorative extra ribs between the diagonal ribs and the transverse arches), and also labels the bosses. Now take a look at the animated diagram, and see how all the vaults are variations on a single theme.

On the next illustration panel, I've separated out the types so you can look at them slowly if you wish. Notice how each variant merely adds more ribs or bosses, while the underlying vault remains the same shape.

Next (page 2), we'll discuss what all these patterns are about.

Page 1: structure and terms
Page 2: an idea is born
Page 3: the patterns and the power
Page 4: problems with towers
Page 5: the masons fight back
Page 6: lilies, seashells, snowflakes and waterfalls
Page 7: Glossary and Dates