Byzantium's Balkan Frontier seems a straightforward title, but it is ambiguous: the meanings conveyed by the three words to a modern reader would not have been recognized in medieval south-eastern Europe. The Byzantines called themselves Rhomaioi, Romans, and their capital ‘New Rome’. Byzantium–from Byzantion, the site on the Bosphorus refounded as Constantinople–was a neologism of the sixteenth century, and its use was essentially pejorative, intended to distinguish the decadent Christian successor from its predecessor, the Enlightenment ideal of Rome. Balkan is a Turkish word for mountain, first applied by the Ottomans to the range known to classical and Byzantine authors as Haemus, and today as the Stara Planina. Balkan was first applied to the whole mountainous peninsula in the nineteenth century. There was no Byzantine collective word for all the lands beween the Danube and the Mediterranean, except as part of a greater whole: Europe, as defined by Herodotus, or–in contexts we will explore further–oikoumene, ‘the civilized world’. The word ‘frontière’, from the Latin ‘frons’, emerged in French to signify the facade of a church, or the front line of troops disposed in battle formation. It came to be used as an alternative to ‘limite’, from the Latin ‘limes’, and by the sixteenth century had absorbed the meaning of the latter; that is, it contained the notion of limitation. However, ‘frontière’ also retained its own connotations of facing and moving forward.