This description applies to gothic architecture generally—in other words, to the styles which rose in northern Europe. The influence of materials on architecture is also worth notice. Where granite, which is worked with difficulty, is the material obtainable, architecture has invariably been severe and simple; where soft stone is obtainable, exuberance of ornament makes its appearance, in consequence of the material lending itself readily to the carver’s chisel. Where, on the other hand, marble is abundant and good, refinement is to be met with, for no other building material exists in which very delicate mouldings or very slight or slender projections maybe employed with the certainty that they will be effective. Where stone is scarce, brick buildings, with many arches, roughly constructed cornices and pilasters, and other peculiarities both of structure and ornamentation, make their appearance, as, for example, in Lombardy and North Germany. Where materials of many colors abound, as is the case, for example, in the volcanic districts of France, polychromy is sought as a means of ornamentation. Lastly, where timber is available, and stone and brick are both scarce, the result is an architecture of which both the forms and the ornamentation are entirely dissimilar to those proper to buildings of stone, marble, or brick. EGYPTIAN ARCHITECTURE. The remains of Egyptian architecture with which we are acquainted indicate four distinct periods of great architectural activity: (1) the period of the fourth dynasty, when the great pyramids were erected (probably 3500 to 3000 B. C.); (2) the period of the twelfth dynasty, to which belong the remains at Beni-Hassan; (3) the period of the eighteenth and nineteenth dynasties, when Thebes was in its glory, which is attested by the ruins of Luxor and Karnak; and (4) the Ptolemaic period, of which there are the remains at Denderah, Edfou, and Philæ. The monuments that remain are almost exclusively tombs and temples. The tombs are, generally speaking, all met with on the east or right bank of the Nile: among them must be classed those grandest and oldest monuments of Egyptian skill, the pyramids, which appear to have been all designed as royal burying-places. A large number of pyramids have been discovered, but those of Gizeh, near Cairo, are the largest and the best known, and also probably the oldest which can be authenticated. The three largest pyramids are those of Cheops, Cephren, and Mycerinus at Gizeh. These monarchs all belonged to the fourth dynasty, and the most probable date to be assigned to them is about 3000 B. C. The pyramid of Cheops is the largest, and is the one familiarly known as the Great Pyramid; it has a square base, the side of which is 760 feet long,[J] a height of 484 feet, and an area of 577,600 square feet. In this pyramid the angle of inclination of the sloping sides to the base is 51° 51′, but in no two pyramids is this angle the same.