Many early 19th-century neoclassical architects were influenced by the drawings and projects of Étienne-Louis Boullée and Claude Nicolas Ledoux. The many graphite drawings of Boullée and his students depict spare geometrical architecture that emulates the eternality of the universe. There are links between Boullée's ideas and Edmund Burke's conception of the sublime. Ledoux addressed the concept of architectural character, maintaining that a building should immediately communicate its function to the viewer: taken literally such ideas give rise to "architecture parlante".