In 1872 Mountfort became a founding member of the Canterbury Association of Architects, a body which was responsible for all subsequent development of the new city. Mountfort was now at the pinnacle of his career. Mountfort notably altered the use of a segmented arch rather than one in the Romanesque style; the latter of which was considered by Augustus Pugin to be fundamentally important to the Gothic style.
In 1872 Mountfort joined as a co-founder of the Canterbury Association of Architects, an organization that handled all future development of the new city. Mountfort was now at the peak of his career. Mountfort is notable for changing the use of segmented arches instead of those in the Romanesque style; the latter were considered by Augustus Pugin to be fundamental to the Gothic style.