access to the lodgings of the troops; the Via Sagularis, within and parallel to the Intervallum, was carried round the whole rectangle. To this general scheme the camps which have been excavated conform, with little divergence.[190] I give as an example the fort at Housesteads, on the Roman Wall (Fig. 21). The sanctuary, X, which is here rectangular, is not infrequently apsed.[191] As a rule not much remains of the interior buildings except the Praetorium and a few large public edifices, such as granaries and armouries. The Praetorium varies considerably in detail, but in general disposition it resembles the Greek peristyle house. A typical, well-preserved example is to be found at Wiesbaden.[192] [Illustration: FIG. 21. Roman fort at Housesteads. (By kind permission of Professor Haverfield.)] One of the most imposing of Praetoria is that of Lambaesis[193] in northern Africa, where a stone-built camp was constructed about the same date as Odhruḥ to replace the older earthwork. The development of the Praetorium varies with the size and importance of the station. As regards the outer fortifications the four gateways were flanked by towers which projected inwards, from the inner face of the wall, and not uncommonly had a slight salience upon the exterior also.[194] There are one or two examples in which the gate towers are rounded upon the outside and have a more considerable projection.[195] Towers are usually placed at the rounded corners of the wall, and sometimes at intervals along the wall; they have no salience upon the exterior.[196] The barracks, which were as a rule roughly built huts, were more solidly constructed in some of the great permanent camps, and the whole interior plan has been traced at Carnuntum and at Novaesium. The barracks in these camps consisted of long double rows of small chambers, more or less regularly disposed and standing back to back. A street or court, open at either end, unless it happened to terminate against one of the larger official buildings, separated each row from the row opposite. The Intervallum was left open, that free access might be given to the walls; at Carnuntum only, part of the west side was occupied by buildings. [Illustration: FIG. 22. Odhruḥ. (From _Provincia Arabia_, by kind permission of Professor Brünnow.)] In the Trajanic camp at Odhruḥ (Fig. 22) no trace of the interior buildings remains except a small apsed Sacellum, placed precisely in the position in which it would be found in a camp on the European frontiers. Since the four gateways compare equally well with those of the European camps, we may conclude that the interior arrangement of Odhruḥ was normal. But the fortifications are not normal. Rounded towers project some ten metres from the outer face of the wall and the angles are strengthened by circular towers of still greater salience. Thus in the earliest camp of the Arabian limes we encounter a developed system of flanking towers which is completely absent in Europe.