§ 43. But, when the question of adding aisles to a church arose, the builders were met by the difficulty that the church was wanted constantly for service. The taking down of the walls and the building of new arcades interfered with this necessary use of the fabric. In our own day a congregation, driven out by builders or restorers, can resort to a school room or mission room. In the middle ages, these alternatives were unknown; and the church was positively indispensable. With this in view, the builders were obliged to add their aisles without touching more of the main fabric than they could help. Usually, then, they took the length of the existing aisleless building for the length of their aisles. They then set out the aisles upon either side of the church, building the outer walls, and dividing them into bays by external buttresses. Then, opposite each buttress, they proceeded to break through the walls of the church. Leaving a piece of the old wall to serve as a footing for each column, they built up the columns in the thickness of the wall, the masonry being gradually removed as each rose in height. The arches were made in the same way, the wall being removed by degrees until the two sides of each arch met at the key-stone. The aisles were then roofed, and, finally, the masses of wall which still remained beneath each arch were broken down, and the nave and aisles thrown into one. The old masonry could be removed through the doorways of the aisles; and sometimes one of the end walls of either aisle was left unbuilt to the last, so that the masons could have free entrance for new, and exit for old, material. The old walls of the nave, above the columns and arches, were left untouched. In this way the upper parts of the walls of several Saxon naves--more, probably, than we have opportunity of discovering--remain to us. The north wall at Geddington in Northamptonshire is the most striking instance. The practice was so common as to be general. In hundreds of country churches the plinths on which the columns of the nave rest are probably pieces of the foundation of the older wall, refaced, or even left in the rough. Instances are nearly as common in which the heads of the new arches have blocked earlier windows; for, in the eleventh and twelfth centuries, when glass was rare and expensive, and the openings were usually closed by latticed shutters, the windows were set high in the wall. There is a remarkable example of the retention of old work at Seamer, near Scarborough. To this fine twelfth century aisleless church a north aisle was added in the fifteenth century. The builders, possibly wishing to avoid expense, employed the old method, which in those days of prosperity and general rebuilding had fallen into disuse. In order not to interfere with the older windows, they deliberately made their arches very low: the result is that, from the interior of the aisle, one can see that the old wall was almost entirely kept, the new columns being built up on the line of the flat pilaster buttresses, which were left unaltered above the capitals. Sometimes, the connexion between nave and aisles was made by cutting arches at intervals in the wall, without building columns. The north arcade at Billingham in Durham, and the thirteenth century arcades at Tytherington in Gloucestershire consist of arches with large masses of the earlier wall left between them. Such a method was economical, as much less dressed stone was required; and we find it employed at Copford in Essex, where good building stone was hard to get. Nevertheless, it prevented the free circulation of light from the windows of the aisles, and practically shut off the aisles from the church.