be drawn which will pass straight from the centre of one buttress to that of the buttress opposite, and will pass through the centre of the intervening columns on its way. [Illustration: Fig. 10. Plan of Raunds church, Northants.] Sec. 48. It already has been shown that builders were very unwilling, in making their additions to churches, to destroy old work altogether. At times they displayed an extraordinary conservatism in their re-use of old material in their new work. This was not invariable. In the splendid churches of south Lincolnshire, during the fourteenth century, their aim seems to have been complete rebuilding; and such examples as the magnificent nave at Swaton, near Sleaford, or the neighbouring church of Billingborough, show how old work must have been swept away by the enthusiasm for lofty arcades, elaborately traceried windows, and walls of dressed stone-work. On the other hand, half the charm of the hardly less beautiful churches of Northamptonshire is the result of the clever way in which the masons dove-tailed all the old stone-work which was worth preserving into their new additions. Such churches as Tansor and Oundle are, for that reason, unexcelled in interest, offering, as they do, almost inexhaustible problems as to the development of their plan. In all parts of England we find that builders, whatever else they destroyed, carefully kept, as a general rule, the doorways, and especially the south doorway, of the buildings which they enlarged. This accounts for the large number of handsome Norman doorways which remain in the walls of aisles obviously later than the doorways themselves. At Birkin in Yorkshire, the south aisle was not built till the middle of the fourteenth century, but the doorway was removed to its new position from the wall of the aisleless church. One very exceptional case occurs at Felton in Northumberland. Towards the beginning of the thirteenth century, the west part of the south wall of the church was cut through, a chapel was added, and, east of the chapel, a porch was built. Rather more than fifty or sixty years later, it was determined to add a south aisle the full length of the nave. The width of the aisle was taken from that of the existing chapel and porch. To connect the chapel with the new work, the side walls of the porch were cut through. The outer doorway of the porch became the new south doorway, while the inner doorway was kept unaltered, as an arch in the new arcade.