Why do we reference centuries a step ahead of the year? For example 1900s – 20th Century?

Question

Why not 20th Century being 2000- 2999?

In: 0

Answer 1

There was no year 0 – we started with year 1. So year 1 thru year 100 was the _first_ hundred years, and thus the _first_ century.

We continue that tradition for every subsequent century, and use the same logic for other groupings, like decades and millennia.