Of the nature of these unlicensed strongholds there is considerable doubt, but a great probability exists that they were of very rapid construction and, therefore, not of the Rectangular Keep type, but of the Motte and Bailey, or of the Shell Keep pattern. That a large amount of time had been spent in their erection seems to be negatived by the fact that upon the accession of Henry II. the great majority of "adulterine" castles were destroyed in the course of a few months. This would have been impossible if solid masonry erections were in question, but hastily improvised defences built by forced, and therefore, probably, unskilled labour, would not present great difficulties. In all likelihood a great number of the earthworks which occur in England, and have not been assigned to any particular date, may owe their origin to this disturbed period, especially those of the Motte and Bailey type. Upon the whole, we can hardly look upon the reign of King Stephen as a period distinguished by an advance in the art of castle-building, but rather as one of temporary retrogression to elementary types. With the advent of the second half of the twelfth century the Castle began to show in many details the influence of the Early English style of architecture, though ornamentation is singularly rare in early castellation compared with the lavish wealth bestowed at the same time upon ecclesiastical buildings. The Norman style was still adhered to in the main outlines, but the external pilasters developed to such an extent that they became buttresses, as at Clun and Dover, the masonry workmanship improved, local stone came more into use, and internal decorations, such as ribs to the vaulting, began to be introduced. It is not uncommon to find the dog-tooth ornament employed in conjunction with contemporary work in the Norman style, but so long as the Rectangular Keep remained, the internal arrangements became, as it were, stereotyped, and were strictly adhered to. The latest styles of Rectangular Keeps carried but few, if any, suggestions of Norman architecture as they trended upon the Early English periods; thus Fonmon Castle in Glamorganshire, and Penhow in Monmouthshire, exhibited no traces of pilaster buttresses, and other features so strongly marked in earlier examples.