The Mammisi exhibit quite a different form of temple from those previously described, and are generally found in close proximity to the large temples. They are generally erected on a raised terrace, rectangular in plan and nearly twice as long as it was wide, approached by a flight of steps opposite the entrance; they consist of oblong buildings, usually divided by a wall into two chambers, and surrounded on all sides by a colonnade composed of circular columns or square piers placed at intervals, and the whole is roofed in. A dwarf wall is frequently found between the piers and columns, about half the height of the shaft. These temples differ from the larger ones in having the outer walls perpendicular. The constructional system pursued by the Egyptians, which consisted in roofing over spaces with large horizontal blocks of stone, led of necessity to a columnar arrangement in the interiors, as it was impossible to cover large areas without frequent upright supports. Hence the column became the chief means of obtaining effect, and the varieties of form which it exhibits are very numerous. The sculptors appear to have imitated as closely as possible the forms of the plant-world around them. In one they represent a bundle of reeds or lotus stalks. The stalks are bound round with several belts, and the capital is formed by the slightly bulging unopened bud of the flower, above which is a small abacus with the architrave resting upon it: the base is nothing but a low circular plinth. The square piers also have frequently a lotus bud carved on them. At the bottom of the shaft is frequently found a decoration imitated from the sheath of leaves from which the plant springs. As a further development of this capital we have the opened lotus flower of a very graceful bell-like shape, ornamented with a similar sheath-like decoration to that at the base of the shaft. This decoration was originally painted only, not sculptured, but at a later period we find these sheaths and buds worked in stone. Even more graceful is the palm capital, which also had its leading lines of decoration painted on it at first, and afterward sculptured. At a later period of the style we find the plant forms abandoned, and capitals were formed of a fantastic combination of the head of Isis with a pylon resting upon it. In one part of the temple at Karnak is found a very curious capital resembling the open lotus flower inverted. The proportion which the height of Egyptian columns bears to their diameter differs so much in various cases that there was evidently no regular standard adhered to, but as a general rule they have a heavy and massive character. The wall-paintings of the Egyptian buildings show many curious forms of columns, but we have no reason for thinking that these fantastic shapes were really executed in stone.