The auxiliary regiments naturally did not fare so well. The small detachments drafted off for service in the field army probably soon lost their identity, and the _castella_, which contained the regimental head-quarters, must have often been taken and destroyed. Still, as the appendix shows, over fifty regiments survived long enough to be included in the _Notitia_. Naturally the chances of surviving had varied on different frontiers. The section of the _Notitia_ which deals with the northern frontier of Britain contains so many names of pre-Diocletianic regiments that it has sometimes been thought to represent the earliest stratum in the whole work. There seems, however, no reason to doubt that the original garrison, although in attenuated numbers, succeeded in maintaining itself until well into the fourth century. We know from archaeological evidence that even the mile-castles were not abandoned until the reign of Constantine.[436] An almost equally large proportion of old regiments is present in the garrison of Cappadocia, which had been spared the full force of the Persian attack.[437] In Egypt, too, most of the old regiments still survive, although they are largely outnumbered by recent formations.[438] The garrison of this important corn-producing province, more essential than ever since the foundation of Constantinople, had evidently been increased to guard against renewed attacks from the Blemmyes on the Upper Nile, who had raided it successfully in the third century. The Rhine frontier, on the other hand, seems to have been swept of its old garrison from end to end. Two of its legions have disappeared, and the other two, which are included in the field army, probably only survive thanks to their names being preserved by detachments which were absent when the fortresses were stormed.[439] It is not until we reach Raetia and the protection of the Upper Danube that any of the old auxiliary regiments appear. On the Middle and Lower Danube, however, the scene of repeated invasions and civil wars during the third century, few of the old troops survived. The struggle was probably a long one: we know from epigraphical evidence that several forts were still holding out towards the end of the century, and excavation may show that many barbarian raids retired without doing any serious damage. But the attack was constantly renewed, and it is not surprising to find that three new cavalry formations have replaced the Cohors Hemesenorum at Intercisa,[440] and that detachments of Equites Dalmatae are now responsible for practically the whole stretch of frontier between Belgrade and Buda-Pesth.[441] Only the Cohors I Thracum C. R. and the Cohors III Alpinorum, the latter of the old Dalmatian army, remain to remind us of the corps which defended this frontier in the second century.[442] On the Lower Danube, where the Goths had crossed in force, and in the oriental provinces which had felt the heavy hand of Persian invader and