On 20 February 1802 Rheinfelden was made a district capital of the newly created Canton of Fricktal , ( Principality of Frickgau ) , joining the Helvetic Republic in August , the point at which the city became decisively Swiss .
On 20 February 1802 , Rheinfelden was made the capital city of the new Canton of Fricktal , joining the Helvetic Republic in August , the point at which the city became mostly Swiss .