Building huge churches and cathedrals is probably the most monumental task humans set themselves.

"My business is to see what will bring people soonest to their knees," said John Loughborough Pearson, architect of Truro Cathedral, and this bald remark sums up the instinct in every monumental builder, though it is usually expressed in more flowery language.

Humans respond to scale. The buildings are high enough to house giants or even trees, while we scuttle about at floor level.

Enclosing such spaces created other awesome effects. Sound, for example – the long plainsong chants which arose in the second millennium are clearly designed to echo and re-echo, singing to the new architecture.

Light was another innovation. Originally, very tall buildings had to be square towers of mass stone, but with the European invention of the Gothic arch, suddenly the proportion of window increased dramatically.

When coloured glass filled the spaces a new vision of wonder was created, and when the heady smoke of incense caught the sloping coloured light, the assault on the senses of the congregation was complete.

But the basic technology was often underlined by some very basic mistakes.

Even with the spacious arches, the weight of these buildings was enormous. This was concentrated most of all on the crossing arches of the transept, which carried the weight of the tower or spire.

Winchester Cathedral was famously so endangered by subsidence that it sent a deep-sea diver down to underpin its structure with concrete.

Others were less lucky, for example Chichester. There were several attempts to save their Sir Christopher Wren spire, the last being in 1861 when the combined weight and friction turned some of the stones to dust, which ran continuously out of huge cracks like water until the whole spire collapsed in on itself.

Cornwall's Nobel Prize-winning William Golding wrote a tense piece of fiction called The Spire, in which a cathedral dean pursues a religious vision by building a huge spire despite the advice of his master builder.

As the spire rises, the top begins to sway, the pillars bend and the arches "sing". These can be frightening buildings.

Fortunately the restorers of Truro Cathedral's spires have less dramatic problems to face, but they are still serious enough. The cathedral was built of Bath stone, a warm light-coloured rock, relatively quick and easy to work.

It was certainly quicker and easier than the granite, slate, serpentine and other native Cornish stones of which older churches were built.

But Cornwall isn't Bath, and the effect of salt, rain, high winds and acidity is clear to see in the stones, some of which have become almost filigree due to weathering.

After only a hundred years – scarcely an adolescence in church-building terms – it's disappointing having to replace stone on such a huge scale.

A better look around could have shown Mr Pearson that the old boys knew best, and perhaps that there are more ways than one to bring people to their knees.