…is a spelling peeve: the confusing duo of capital and capitol.
Capitol is the building: The state capitol is an imposing granite structure with a golden dome.
Capital is the city that’s the seat of government for a country or state or similar region. The paperwork needs to be sent to the state capital.
Capital is also the spelling for just about every use of the word that doesn’t refer to the big building with the fancy dome. Usually, these words have something to do with being at the top or the head of something: capital ships are the most important ones in the fleet; capital funds and assets are the ones you start with; capital crimes are the ones that you could lose your head over; and so forth.
As for the fact that the state capitol is usually in the state capital . . . these things are sent to test us, and to remind us that while the spellchecker may be our good friend, it’s not necessarily our most reliable friend.