In such a clearance it was impossible to preserve all the structures. Had Petrie and his companions avoided moving the foundations of the twenty-sixth dynasty, they could never have seen much of the earlier work; had they left the paving of the twelfth dynasty in place, they must have sacrificed the objects of the Old Kingdom. [Illustration: 393.jpg GENERAL PLAN OF BUILDINGS AT ABYDOS] Also, had they only worked the higher levels, and left the rest, the inflow of high Nile would have formed a pond, which would have so rotted the ground that deeper work could not have been carried on in the future. The only course, therefore, was to plan everything fully, and remove whatever stood in the way of more complete exploration. All striking pieces of construction, such as the stone gateways of Papi, were left untouched, and work carried on to deep levels around them; in this way, at the end of the season, the site was bristling with pieces of wall and blocks of stonework, rising ten or fifteen feet above the low level clearances. As the excavations progressed, there was an incessant need of planning and recording all the constructions. Professor Petrie always went about with a large dinner-knife and a trowel in his pocket, and spent much time in cutting innumerable sections and tracing out the lines of the bricks. The top and base level of each piece of wall had to be marked on it; and the levels could then be measured off to fixed points. An outline of some of the principal buildings is given, to show the general nature of the site of the temple of Abydos. This plan is not intended to show all periods, nor the whole work of any one age; but only a selection which will avoid confusion. The great outer wall on the plan was probably first built by Usirtasen I.; the bricks of the oldest parts of it are the same size as bricks of his foundation deposits, and it rests upon town ruins of the Old Kingdom. But this wall has been so often broken and repaired that a complete study of it would be a heavy task; some parts rest on nineteenth dynasty building, and even Roman patchwork is seen. Its general character is shown with alternating portions, the first set consisting of towers of brickwork built in concave foundations, and then connecting walls between; formed in straight courses. The purpose of this construction has long been a puzzle. The alternate concave and straight courses are the natural result of building isolated masses, on a concave bed like all Egyptian houses, and then connecting them by intermediate walls. The hard face across the wall, and the joint to prevent the spread of scaling, are the essential advantages of this construction. The corner marked Kom-de-Sultan is the enclosure which was emptied out by Mariette 's diggers, because of the abundance of burials with steles of the twelfth to eighteenth dynasties. [Illustration: 395.jpg WALL OF USIRTASEN I.]