The Jire?ek Line is a conceptual boundary through the ancient Balkans that divides the influence of the Latin (in the north) and Greek (in the south) languages in the Roman Empire from Antiquity until the 4th century. A possible rough outline of it goes from near the city of Laçi in modern Albania to Serdica (now Sofia, in Bulgaria) and then follows the Balkan Mountains to Odessus (Varna) on the Black Sea or continuing along the coastline northwards to the Danube Delta. However, the proposed line, in its various forms, is a theoretical tool only: Latinized groups live south of the line (such as the Aromanians, Meglenites, Cutzovlachs (Kutzo-Vlachs), and Moscopolitans) and Hellenized ones north of the line (e.g. by the Greek colonies along the western coastline of the Black Sea). Even so, it is a useful -- although approximate -- instrument for determining which influence a certain area was predominantly exposed to. The placement of the line is based on archaeological findings: most of the inscriptions found to the north of it are written in Latin, and most of the inscriptions found to the south of it are in Greek.
It was originally used by Czech historian Konstantin Jire?ek in 1911 in a history of the Slavic people.
More recent scholars have revised it somewhat: Kaimio (1979) places Dalmatia and Moesia Superior in the Latin area and Moesia Inferior in the Greek sphere. MacLeod (1982) suggests that there may not have been "an official language policy for each and every aspect of life" but that "individual Roman officials [made] common sense ad hoc decisions". He also points out that while the area was under Roman rule, "even in Greek areas... Latin was the dominant language in inscriptions recording public works, on milestones, and in the army".