Perspective in general is a means of constructing a convincing impression of three-dimensional space on a two-dimensional surface. Linear perspective primarily uses line to produce this effect. Aerial perspective, however, primarily uses tone and colour. The best known system of linear perspective is that described by Alberti in his treatise 'On Painting' ('De Pictura', 1435), in which receding parallel lines appear to converge on a single point on the horizon.