The study of mediæval architecture is one of the most fascinating of pursuits, but it is one beset with difficulties. The obscurity in which the origin of our great monuments is buried is profound and often impenetrable. A fertile cause of error is the confusion which in many cases has arisen between the dates of foundation and of consecration. Very often a church was built and afterwards considerably modified, rather than actually reconstructed, on the same consecrated site. Lightning was the most frequent cause of the destruction, total or partial, of mediæval churches. Striking the steeple, the tower, or the roof, it fired the timber superstructure of the nave. This in itself would not have been an irreparable disaster; but as the timbers gave way the calcined beams charred the piers, and so prepared the downfall of the whole building, which was then either restored or reconstructed in the fashion of the day. Hence, whether we base our deductions upon more or less trustworthy records or upon contemporary readings of existing data, the result is too often a confusion among vanished monuments, or a contradiction between the buildings as they now exist and the historic records which relate to them. [Illustration: 32. CATHEDRAL OF LAON. PLAN] [Illustration: 33. CATHEDRAL OF LAON. INTERIOR OF THE NAVE] Nothing is easier for interested theorists than to post-or ante-date the structure of a building. They have nothing to fear from the testimony of writers, and, with very few exceptions, it is difficult to assign a precise date to the construction of great churches and cathedrals or to point with certainty to their architects. The obscurity of these great artists is perhaps to be accounted for by the fact that they were ecclesiastics. As such the honour of their achievements belonged not to the individual, but to the corporate body, the _order_ of which they were members, and members moreover who had, in most cases, taken the vow of humility. Modern science, architectural and archæological, has failed to throw much positive light on this subject. It contents itself for the most part with ingenious hypotheses and learned deductions which leave us still in doubt as to precise dates. But we shall at least find some sort of foothold in a careful architectural survey of buildings themselves. This should be, of course, supplemented by study of historic records, and such a study will convince us that art in the Middle Ages, as in all epochs, obeyed the immutable laws of filiation and transformation. We shall follow the artist step by step, observing his research, his hesitation, his errors, and even his corrections.