In terms of architecture, intercolumniation refers to a system of horizontal spacing between two adjacent columns of a colonnade. In Baroque, Classical and Renaissance Architecture, intercolumniation was done by resorting to a device which was developed by the renowned Roman Architect Vitruvius who lived in the 1st Century. The diameter of the columns was taken as the unit of measurement. The five standard intercolumniation measurement set out by Vitruvius are 11/2 diameter interval (D), called pycnostyle intercolumniation; 2D, called systyle; 21/4D (the most common ratio), called eustyle; 3D, called diastyle; and 4 or more D, called araeostyle.