The capitol in the capital on capitol hill, down the parkway past the park. No, the park park, not the car park. English is a fun language. No opinion on the English though.
"Capital" comes from the Latin word for "head"; leading cities that have historically dominated their neighbors became known as capitals because they were the "heads" of their regions.
"Capitol" comes from the name of the Capitoline hill, at the center of Rome.
Capitol is the building in which a legislature meets. eg: The Capitol Building.