Galileo begins the first day of Dialogues Concerning Two New Sciences by relating several stories of contemporary structural failures that were inexplicable within the state of the art of Renaissance engineering. As indicated in the last chapter, several of the stories have to do with the problem of proportionately similar structures behaving differently depending upon whether they are large or small, hence manifesting a scale effect. According to Galileo,

Such generalizations could, of course, be reached by experience alone, and there were no doubt even rules of thumb as to how large an obelisk or column had to be to require special care in its storage or erection. Empirical evidence of failure and rules of thumb were not sufficient to explain why a failure would occur, of course, but they could certainly help avoid failures in situations recognized to be precarious. Indeed, with little more than an empirical understanding of what worked and what could go wrong when the untried was tried, Renaissance designers might have been particularly cautious in their attempts to extrapolate to larger structures and ever attentive to situations that might lead to failure.