Space between the lower parts of the shafts of adjacent columns in a Classical colonnade or portico defined by modules the same size as the shaft diameters (d below). Vitruvius described its commonest varieties:1–2d:pycnostyle (used only with the Ionic and Corinthian Orders);2d:systyle;–4d:eustyle (usual Roman and Renaissance spacing, with 3d used for the wider central intercolumniation of a portico);3d:diastyle;more than 3d:araeostyle.Perrault is supposed to have invented araeosystyle, an arrangement with two columns – 2d apart followed by a space of 3–2d used at the east front of the Louvre, Paris, and also by Wren at St Paul's Cathedral, London. Doric intercolumniation is not controlled by diameters, but by the relationships of triglyphs and metopes. Greek Doric Hellenic intercolumniation normally had one triglyph over the space between columns (therefore of the monotriglyph type), and, of course, one on the centre-line of each column, although the Propylaea in Athens has two over the entrance. Hellenistic intercolumniation was generally wider (even in Doric), often with two (ditriglyph) or more triglyphs above, giving a lighter, more elegant appearance. At the angles of Greek Doric porticoes, however, because the end triglyphs must terminate each frieze and therefore touch at the corner, the corner-columns cannot be placed on the centre-line of the triglyphs, and have to be moved inwards, so that the adjoining intercolumniations are smaller than usual. This problem does not exist in Roman or Renaissance Doric, as the triglyphs do not touch at the corners, so the corner-columns can be on the centre-lines of both corner-triglyphs, and a half-metope is set on each face of the angle.
1–2d:pycnostyle (used only with the Ionic and Corinthian Orders);
–4d:eustyle (usual Roman and Renaissance spacing, with 3d used for the wider central intercolumniation of a portico);
more than 3d:araeostyle.
J. Curl (2001);Dinsmoor (1950);Gwilt (1903);D. S. Robertson (1945);Vidler Placzek (ed.) (1567)