As anyone who has looked at the subject is aware, many different explanations have been put forward for the fall of the Western Empire. Some authors have stressed the barbarianisation of the army, some the settling of barbarians within the provinces, while others opt for economic or demographic decline, or even the effects of the rise of Christianity.

I personally believe that all of these featured in the decline of the west, yet I also feel that another factor needs to be taken into account; therefore I propose the hypothesis that the division of the provinces and the reorganisation of the administration at the end of the third century contributed to the fall.

The reforms, usually attributed to Diocletian - although for the purpose of this discussion the question of who was the actual author is irrelevant - are usually seen as being one of the major reasons behind the recovery of the empire following the so-called 'third-century crisis'.  The theory is that by shrinking the size of the provinces it was made easier for provincial governors to administer them, whilst at the same time the division of military and civilian roles, and the fact that provincial generals had fewer troops under their command, resulted in a decline in the provincial generals' ability to bid for the Purple.

In theory, however, the same factors that should make rebellion more difficult can also be interpreted as a hindrance when it came to facing raiders crossing the border into Roman territory. These incursions were likely to be based on speed of movement, in order to both be able to penetrate the empire’s defensive borders and also allow a successful retreat with a large amount of booty. Consequently, speed was also essential if the Romans were to mount the appropriate response.

However, it is possible to see the new system as reducing the reaction time of the defenders. First, the general would need to spend time liaising with the civilian governor in order to arrange for supplies to be available at appropriate depots for the pursuing troops should the pursuit become prolonged. In a 'best-case' scenario, there would actually be no delay in these arrangements as the governor and the general act in accord. Yet there is reason to believe that this may not always have been the case.

The inefficiency of the system is possibly illustrated by Ammianus Marcellinus. At xiv, 10.4 of ‘The Histories’, the general Rufinus has to explain to troops waiting to go on campaign against the Alamanni why the supplies have not yet arrived.  Yet most modern authorities do not appear to accept the concept that the Roman system could be inefficient, and so it is not taken into consideration.

The causes of such delays could be varied. Not only was there the possibility of personal or political friction between the general and the governor, there was also the chance of the division of command leading to disagreement on the subject of the best method of response.  

For example, the general may wish to pursue a group of raiders within the province. However, the governor may be apprehensive about the possibility of another, larger party attacking whilst the general is otherwise engaged. He may even fear the consequences of a military defeat. Therefore, he may want the troops to be kept in place in the city as a precaution. The ensuing discussions could lead to delay, if not inaction, and so result in a successful raid which would in itself encourage further attacks.

There is also the factor that the new provinces were smaller and, in several cases, thinner  than the previous ones. Consequently raiders would take less time to pass through and the they would therefore reach the inner, comparatively undefended provinces relatively quickly.  Any delay in the detection and interception of the raiders, such as that suggested above, would therefore be likely to let them pass unopposed through the border province.  Of course, this eventuality would result in further problems should the border force want to pursue across provincial boundaries.