In Germany the crypt is often raised sufficiently above the level of the ground to obtain light from windows, as at Spires, and this is sometimes carried to such an extreme that the church becomes double, that is, of two stories, as at Schwartz Rheindorf. In England, Canterbury Cathedral possesses perhaps the best example, the crypt being very large and its details varied. Some of the capitals of the columns remain half finished, the work upon them having been arrested by a conflagration in the twelfth century. X. GOTHIC ARCHITECTURE. Briefly recapitulating the preceding chapters: We have seen that the Greek temple, composed of a cella, or oblong room, surrounded by a colonnade, was copied by the Romans with but few alterations, the only one of importance being the addition of a semicircular recess to the rear wall. The columns of the colonnade having been transposed from the outside to the interior, dividing the room in three parts, longitudinally; a cross wall having been introduced dividing it transversely, and the apse retained, the building became a basilica. By extending the transept and nave the plan became cruciform and symbolically the most suitable for that of a Christian church. The Western architects, desiring to replace the wooden roofs by stone vaults, found it convenient to substitute for columns carrying arches, piers with engaged shafts connecting directly with the superstructure. After various attempts to obtain direct light for the central division or nave, rendered difficult by the necessity of counteracting the continuous thrust of the barrel vault thrown across it, this vault was finally abandoned and replaced by intersecting vaults, which conveyed the thrust diagonally upon equidistant piers. To avoid increasing the size of the latter to an inconvenient extent, an expedient was resorted to which consisted in propping them from the exterior by flying buttresses thrown from them to outside piers across the roof of the aisles. The result of the width of the nave being usually greater than the distance between piers was that, while the diagonal ribs of the vault remained semicircular, their lateral intersection produced pointed arches. This form of construction was developed during the middle and latter half of the twelfth century. The pointed arch had been used occasionally before by the Romanesque architects; it had been used frequently by the Arabs, as far back as the eighth century, and had been known and employed long before the Christian era in the sewers of Babylon. It was, therefore, not a new invention, but a known method adopted in a fresh departure in constructive architecture; for the circular arches being abandoned and definitely replaced by the pointed arch the succeeding architecture became pointed or Gothic.