The incidence of the levy upon different provinces can best be judged by a statistical table giving the number of regiments raised in each. This is not easy to construct owing to the confusion caused by the duplication of numbering, and the consequent danger of counting the same corps twice over, or of reckoning two corps as one. There were, for example, in Pannonia two cohorts, each bearing the title ‘I Alpinorum’, which can fortunately be distinguished from one another because they are both mentioned in the same diploma, but there are scores of similar cases which can only be decided as yet on a balance of probabilities. This extremely inconvenient system seems to be due to two causes. In the first place, when new regiments were raised some time after the original levy they seem to have begun a fresh series instead of being included in the old ones. This process can be followed most clearly in the case of regiments raised after 70, which were distinguished by a title derived from the name of the reigning emperor. Thus we have cohorts I and II Flavia Brittonum, I Ulpia Brittonum, I Aelia Brittonum, and I Aurelia Brittonum.[161] Secondly, it seems probable that when newly-raised regiments were drafted into different provinces they were numbered in a different series in each province. This suggestion is supported by the fact that where a regiment bearing a high number is found, it generally appears that the rest of the series was originally stationed in the same province, whereas isolated cohorts generally have a low number. For example, the greater part of the Gallic levies were originally stationed on the Rhine. Consequently, we find few duplicate numbers and several series which run up to four or even higher. The Thracian regiments, on the other hand, on account of their special utility as archers, were distributed very widely throughout the Empire during the first century, and of the twenty-seven corps known to us, seventeen are numbered I or II, and are distributed over eight provinces. Apart from this difficulty the following list contains in any case more regiments than ever existed at any one time. Fresh regiments must have been raised to fill the gaps caused by such disasters as the defeat of Varus and the rebellion of Boudicca, but in only a few cases can we distinguish the earlier from the later levies. It is only possible to put in a separate class those regiments which bear a title derived from the Flavians or later emperors, and were probably raised after 70. Still, if these limitations are borne in mind, the following table may serve to show approximately the quota which each province contributed: