From the late 500s, non-Christian populations of Slavs, Avars and other non-Christian peoples had moved into large areas of the Balkans right down into what is now Greece. As a result, the system of bishoprics collapsed (e.g. the bishopric of Sirmium in modern-day Serbia), although some Christian presence remained. From the point of view of Constantinople, this became a "Scythian wilderness." The process of reclaiming this area for the Empire and also for the Christian faith is sometimes referred to as "Reconquista". These lands were Hellenised, imperial control reasserted, and the Eastern Orthodox faith spread. This took place from as early as the mid-600s and continued into the 800s, particularly under Emperor Nicephorus I. Later, evangelist-monk Nikon Metanoite (d. 998) continued the work of reclaiming and re-evangelising Orthodox areas inside the boundary of the Empire ("limes") such as southern Greece, as well as areas where Orthodox had converted to ...