Professor Delbrück is of opinion that the impulse towards decorating the wall-face with the similitude of plastic architecture was quickened by Greek painting, which, from the fourth century B.C. onward, gained an increasing mastery in the representation of spatial dimensions. Plastic examples of the phase of development represented by the Boscoreale frescoes might be expected in the second century B.C., and in fact there were at that period mock colonnades in relief, such as the Ephebeum at Priene. The cutting away of the wall-face by means of niches was foreshadowed in Hellenistic art; the lightening of the wall-mass by niches has been noticed in the gate at Perge and the tombs of Alexandria, while windows in the intercolumniations were of frequent occurrence.[295] It is possible, as Professor Delbrück suggests, that in Hellenistic Mesopotamia decoration by means of blind openings, whether doors, windows, or niches, won a great popularity because it was based on pre-Hellenic tradition, and it is interesting to observe that the only early examples of the arched niche, which is the leading motive at Ukhaiḍir, are to be found in western Asia.[296] But the systematic application of these principles to the façade was accomplished only in the latest phases of Hellenistic art, and we may perhaps owe it to Roman builders. In the intercolumniations of the decorated zone niches, arcades and windows take the place of the traditional moulding,[297] and the upper wall is broken by a row of arches or of windows.[298] On inner walls a double row of niches is sometimes accompanied by stucco incrustation,[299] while the podium is decorated with engaged columns.[300]