The Norman piers had been frequently circular or polygonal, but sometimes nearly square, and usually of enormous mass. Thus, at Durham (Norman), oblong piers of about eleven feet in diameter occur alternately with round ones of about seven feet. In transitional examples columns of more slender proportions were employed either (as in the choir of Canterbury) as single shafts or collected into groups. Where grouping took place it was intended that each shaft of the group should be seen to support some definite feature of the superincumbent structure, as where a separate group of mouldings springs from each shaft in a doorway, and this principle was very steadily adhered to during the greater part of the Gothic period.[14] [Illustration: FIG. 15.--HOUSES AT LISIEUX, FRANCE. (16TH CENTURY.)] Through the E. E. period groups of shafts are generally employed; they are often formed of detached shafts clustering round a central one, and held together at intervals by bands or belts of masonry, and generally the entire group is nearly circular on plan. In the succeeding century (Dec. period) the piers also take the form of groups of shafts, but they are generally carved out of one block of stone, and the ordinary arrangement of the pier is on a lozenge-shaped plan. In the Perp., the piers retain the same general character, but are slenderer, and the shafts have often shrunk to nothing more than reedy mouldings. The column is often employed in Transitional and E. E. churches as a substitute for piers carrying arches. In every period small columns are freely used as ornamental features. They are constantly met with, for example, in the jambs of doorways and of windows. Every column is divided naturally into three parts, its base, or foot; its shaft, which forms the main body; and its capital, or head. Each of these went through a series of modifications. Part of the base usually consisted of a flat stone larger than the diameter of the column, sometimes called a plinth, and upon this stood the moulded base which gradually diminished to the size of the shaft. This plain stone was in E. E. often square, and in that case the corner spaces which were not covered by the mouldings of the base were often occupied by an elegantly carved leaf. In Dec. and Perp. buildings the lower part of the base was often polygonal, and frequently moulded so as to make it into a pedestal.[15] The proportions of shafts varied extraordinarily; they were, as a rule, extremely slender when their purpose was purely decorative, and comparatively sturdy when they really served to carry a weight.