This refers to a document known as the Notitia Dignitatum, a Late Roman document. Meaning (roughly) "List of Dignities" in Latin (as government positions were referred to as dignities or honors), the Notitia outlines the structure of Late Roman bureaucratic administration, as well as the principal frontier commands and regional field armies, for both the Western and Eastern halves of the Empire. As the Western half was written later than the Eastern (roughly the 420's-430's compared to the 390s), it's arrangements are a bit more suspect, but in general the Notitia provides a unique portrait of Roman administration, though the exact dates of compilation are unknown. Most interestingly, images of the insignia of senior officers and [shield patterns of army regiments] (http://lukeuedasarson.com/NotitiaPatterns.html) have survived, through Medieval copies of the document.

Although the Notitia is useful when examining the structure of Roman government (especially it's rigidly hierarchical organization) it is not without it's flaws. Specifically, the text does not describe the numbers of lower-level bureaucrats and unsalaried juniors (supernumerarii) assigned to specific provinces; nor, in it's listing of units for the field armies, does it provide estimates of unit strength. It also ignores completely the regiments of limitanei which garrisoned the frontiers (and which comprised roughly half the army, if not more). As the Western half was compiled later than the Eastern, it is also difficult to determine the accuracy with which military deployments for the West reflected conditions on the ground. As with any primary source, the Notitia Dignitatum cannot be taken at face value, but compared with other source material to determine the validity of it's contents. That said, the Notitia is a remarkable text, and one which is critical to anyone studying the structure of Late Roman administration.