INTERCOLUMNIATION, in architecture, the distance be tween the columns of a colonnade; usually defined by the number of times in which the bottom diameter of the column is included in the distance between the two closest points on adjacent columns. Thus the distance between the centre lines of two columns is one diameter more than their intercolumniation. The intercolumnia tion of classic columns was systematized at an early date and the following standard intercolumniations have been listed by Vitru vius and others : (a) pycnostyle, equal to one and a half diam eters ; (b) systyle, 2 diameters ; (c) eustyle, 2 and a quarter diam eters, so-called "well-columned," as the one most generally satisfactory; (d) diastyle, 3 diameters; (e) areostyle, 4 diameters; and (f) areosystyle, a complex form in which the columns are arranged in pairs with the distance between the pairs greater than the distance between the columns of each pair, as in the colonnade of the Louvre, Paris (by Claude Perrault, 1665). No such abso lute standardization of intercolumniation as Vitruvius' list would suggest exists in classical work; frequently all the intercolumnia tions of a single colonnade differed, with the widest in the centre. The list must therefore be considered, like the so-called rules for the orders, merely as a summary of the averages.