Well, Charles-Louis de Secondat Montesquieu was certainly biased regarding the Byzantine Empire which he referred to as an Imperium Graecorum or Empire of the Greeks. Montesquieu also harbored the typical Enlightenment disgust [Shared with Charles Lebeau, Edward Gibbon and Voltaire] with the Byzantines which he referred to as being an avaricious, decadent, corrupt, bigoted and superstitious people.

Montesquieu derived his knowledge of the growing disunity, weakness and lethargy of the Roman forces from the classical Roman authors. One has only to read the work of the Roman historian Ammianus Marcellinus to see a detailed account of the decay of the Roman military particularly after the disastrous battle of Hadrianopolis which occurred in 378 CE.