castrum measured , was precisely aligned with the cardinal points, had a square floor plan, and covered an area of approximately . The building material consisted for the most part of tephrite, a type of volcanic rock found in the area. The Roman unit of measurement used in the construction could be determined on the basis of still intact, mortared brick slabs. It was exactly , and thus corresponded to two Gallic pedes Drusani—about . The unusual construction of this fort resembles a much smaller facility of the same time period in the Pfalzel district of Trier (Roman Augusta Treverorum), which has been known as the palatiolum since the Middle Ages. There are clear indications that it was furnished with splendid interior decoration, for example mosaics, and thus could have had a primarily ceremonial function. Similar finds are missing for Oedenburg-Altkirch, but it could have been designed by the same architect. Defenses The surrounding wall, three meters wide and carefully laid out and mortared, was reinforced with fourteen square bastions, four on each of the long sides and three on the narrow sides. The dimensions of each bastion were almost identical. The masonry was partially preserved up to a height of . The foundations sat on rammed wooden piles that reached into the masonry, and were reinforced at the edges with rectangular beams connected by crossbars. The wall was filled with layers of rubble that had been mixed with lime mortar. The partition walls, on the other hand, were also set on a bed of lime mortar reinforced with beams. These foundations were first observed on watchtowers in Switzerland dating back to 371. The southwest corner had been severely disturbed by the intrusion of a bunker of the Maginot Line. The outer façade, presumably originally up to high, had an impressive staggered depth due to the tower-like bastions that protruded about five meters and were wide. The corner bastions were created by continuing and superimposing the respective lines of the wall. As a result, two square tower bastions, which had been built at an angle of 90 degrees, were the same size as the central ones. The inner chambers had a side length of . They led into niche rooms half as large, the entrances of which were vaulted by arches supported on pillars. Together with these the fort encompassed an area of . To an observer standing in front