In defence of the system it would probably have been urged that on every frontier the hostile forces were equally dispersed and far less easily concentrated, and that a combination of the Celtic or Teutonic tribes would be heard of long before it was ready for action. The existence of the league which attacked and for a time broke through the Danube frontier in the reign of Marcus was certainly known to the imperial government, and the local governors succeeded in delaying the crisis until the return of the _vexillationes_ which had been sent to the eastern frontier, with whose aid they hoped to be able to cope with the situation.[347] Their calculations were upset by the havoc wrought in the army by the plague which these troops brought with them. Even so the danger was eventually surmounted, and the frontiers were on the whole successfully maintained for nearly a century more. But the full consequences of this system cannot be perceived without some consideration of the changes which it brought about in the conditions of military life and their effect upon the general morale and condition of the troops. A very important point to notice is their immobility. Already in the first century there was, except for the officers, no regular system of transfers, and only an important change in the military situation caused troops to be sent from one province to another. In fact such changes were frequent, and considerable transfers took place, particularly during the Flavian period and the wars of Trajan. From the accession of Hadrian onwards, however, such movements cease almost entirely. During the following hundred and twenty years hardly a legion changed its position and the auxiliary regiments remained almost equally stationary.[348] We can trace regiments which remained literally for centuries in the same province and for the greater part of the time were in the same _castellum_. Of the twenty-one cohorts and alae which are mentioned by the _Notitia Dignitatum_ as forming part of the garrison of Britain, fifteen are shown by the evidence of diplomata to have been in the province long before the end of the reign of Hadrian; and two more, which occur in a diploma of 146, are probably only not mentioned earlier because they were creations of that emperor and had consequently no veterans ready for discharge until after his death.[349] Similarly the Cohors V Lucensium et Callaecorum was in Pannonia at least from 60 to 198, the Cohors I Hemesenorum from 138/46 to 240, and the Ala III Augusta Thracum from 148 to 268/71.[350] The best instance, however, is that of the Cohors II Ituraeorum Felix. This regiment is placed by the _Notitia_ in Egypt, and other evidence shows it to have been in the province in 147, 136, 98, 83, and probably 39.[351] As this section of the _Notitia_ seems to date, at the earliest, from the beginning of the fifth century the regiment was probably quartered in the same province for at least three hundred and twenty years.[352]