These formidable façades were practically fortifications, but the _Merveille_ was further defended to the north by an embattled wall, flanked by a tower which served as a post for watchmen, to which the covered ways running round the base of the western buildings converged. In the middle, on a level with the north-west angle of the _Merveille_, a _châtelet_, or miniature keep, now destroyed, guarded the rugged passage between embattled walls which led to the Fountain of St. Aubert, and was known as the _Passage du Degré_ (passage of the stairway). The various buildings of the abbey which were added in the fourteenth century, after the construction of the _Merveille_, are: the abbot's lodging, with its offices on the south, and certain military works which completed the defensive system. In the fourteenth and fifteenth centuries these were gradually extended to the walls of the town, as we shall see in Part III., "Military Architecture." PART III MILITARY ARCHITECTURE CHAPTER I CIRCUMVALLATION OF TOWNS The distinctive character of military architecture in the Middle Ages must be sought in defensive fortification. In all other respects its constructive methods were identical with those employed in architectural works generally. The few ornamental features of military buildings, as, for instance, the interior vaults and the profiles of consoles and cornices, diverge but slightly from the accepted types of such features in the churches, monasteries, and domestic structures of the period. The Latin, Roman, Gallo-Roman, Romanesque, and Gothic architects were versed in every department of the art they practised. The same architect was called upon to construct the church and the fortress, the abbey, and the ramparts which were often its necessary complement, the donjon, and castle, the town hall, the hospital, the rural barn, and the urban dwelling. He was responsible not only for the inception of every class and form of building, but for its successful elaboration; on him alone the responsibility of its execution rested; no scientific specialist checked his conclusions and verified his calculations as in our own time. The system by which the architect and the engineer have each their separate functions and responsibilities in the construction of the same building was unknown. The builder, or mason, as some would have him called, was an architect in the fullest sense; he himself traced the diagrams of his conceptions, and directed the execution of every detail, careful alike of stability and beauty. [Illustration: 163. ABBEY OF MONT ST. MICHEL. GATE-HOUSE]