What I'd like to know is where in history the idea of having a bold variant of a typeface came about.
I suspect that back in Garamond/Caslon's time there would not have been any bold version of their type, even though modern Garamond and Caslon fonts tend to include bold variants. But I have failed to find out whether this is true or when having a bold variant in typography (for the purpose of emphasis within text) came into being.
I know that giving emphasis with a thicker stroke goes all the way back to hand-lettering days, but haven't heard if this was ever true for the first few centuries of type.
Wikipedia's otherwise great History of Western Typography article has failed me here.