It's disingenuous to read my comment as saying no theory existed, ever. It should be obvious that when you talk about theory covering a product, there either i

It's disingenuous to read my comment as saying no theory existed, ever. It should be obvious that when you talk about theory covering a product, there either is a theoretical framework, or there isn't. In the case of suspension bridges there wasn't. There was no mathematical theory to explain how the bridge stayed aloft, or how much it could carry. What bridge builders of high quality did, was make mock (small) models. And test how much rocks they could put on them. I think you will concede that that isn't a theoretical model. It's a practical one. And this happens very often. People experiment and build useful things, but no one understands why they work. Until later people come along and explain the phenomenon.