 Before the 19th century only one geometry was studied in any depth or thought to be an accurate or correct description of physical space, and that was Euclidean geometry. The 19th century itself saw a profusion of new geometries, of which the most important were projective geometry and non-Euclidean or hyperbolic geometry. Projective geometry can be thought of as a deepening of the non-metrical and formal sides of Euclidean geometry; non-Euclidean geometry as a challenge to its metrical aspects and implications.