In the sixteenth century the troubled reign of Queen Mary was unfavourable to architecture, but towards the end of it the rise of Renaissance art began to exert a decided influence, especially on details and internal furnishings, and in the next century gradually but completely dominated the spirit of the art. Another influence at work was the progress made in artillery. The ordinary castles could not now resist artillery fire, and all attempts at making them impregnable fortresses were abandoned, and the only fortifications retained were such as would make the buildings safe from sudden attack. In consequence, what had before been grim fortresses were now transformed into country mansions, whether on the keep or on the quadrangle plan; and sites were chosen as providing shelter from the elements rather than defence against human foes. The Reformation, too, which secularised the church lands and gave the lion’s share to the nobility, was a notable influence in revolutionising architecture. The nobility being now more wealthy were enabled either to extend their old mansions or to build new ones. Hence the great development that took place in the quiet reign of James VI. The effect of the Union in 1603, which drew many of the nobility to England, was civilising and educative, and raised their ideas of house accommodation as well as their standard of comfort and domestic amenity. The change was of course gradual. The old keeps and the castles built round a courtyard were still in evidence, but picturesque turrets corbelled out at every angle of the building, slated, and terminating in fanciful finials, became the rule. The lower walls were kept plain, the ornamentation being lavishly crowded only on the upper parts. The roofs became high-pitched with picturesque chimneys, dormer windows and crow-stepped gables. All these features so characteristic of the mansion-houses of the fourth period (1542-1700) are well marked in Craigievar, which is one of the best preserved castles of the time. Its ground plan is of the =L= type, but the turrets [Illustration: Craigievar Castle, Donside] and gables are corbelled out with ornamental mouldings and the upper part of the castle displays that profusion of sky-pointing pinnacles and multifarious parapets which mark the period. The same is seen at Crathes and at Castle Fraser. The last is altogether an excellent specimen. It consists of a central oblong building with two towers at the diagonally opposite ends, one square and the other round, and is therefore a development into what has been called the =Z= plan or stepped plan—induced by the general use of firearms in defence. Here, as at Craigievar, gargoyles originally used to carry off rain water from the roof are brought in as a piece of fanciful decoration, apart from any utilitarian purpose, and project from the walls at places where rain-spouts are irrelevant. [Illustration: Crathes Castle, Kincardineshire]