The central battery logic of pre-dreadnoughts

What is the defining feature of a pre-dreadnought?

It combines heavy guns for range with a strong rapid-firing secondary battery intended for closer fighting.

The answer defines the pre-dreadnought through the relationship between a small number of heavy guns and a much larger rapid-firing secondary battery. The heavy weapons could engage at the longer ranges of the period. The ship was then expected to close until its medium-calibre guns could deliver a high volume of fire. That tactical logic, often embodied in a central or casemate battery, differs from the uniform heavy battery associated with the dreadnought.