Correct spelling capitol or capital

Which spelling is correct? "capital or "capitol"?

The word "capital" is derived from the Latin "caput" which meant a head. From this we can see why we have a capital letter at the start or "head" of a sentence. The word was also applied to the head city of a country where its administrative center was usually located. Our body's head is the administrative centers of our bodies which makes it an apt metaphor. In the United States of America the main legislative building is known as the "Capitol" and it stands on Capitol Hill.

Although you will often find people using them interchangeably, it is probably better to use "capital" in general usage and leave "capitol" for buildings.