The Roman road built in the 2nd century BCE that connected the Adriatic Sea with Byzantium was the Via Egnatia.
Constructed by the Roman Republic, the Via Egnatia crossed Illyricum, Macedonia, and Thrace through territory now divided among Albania, North Macedonia, Greece, and European Turkey. Its western terminus was Dyrrachium, modern Durrës, on the Adriatic coast; its eastern route reached Byzantium, later Constantinople and now Istanbul.
The road linked Roman settlements and military centers across the southern Balkans. It crossed difficult mountain terrain, passed near Lake Ohrid and Thessalonica, and extended for roughly 1,120 kilometers. Milestones identify Gnaeus Egnatius, a Roman proconsul of Macedonia, as the official associated with its construction, although the exact building date remains uncertain.
The Via Egnatia was more than a transport route. It connected the Roman world in Italy with the eastern Mediterranean and served armies, merchants, officials, and travelers. The apostle Paul used part of it on his journey from Philippi to Thessalonica. It is sometimes confused with the Via Appia, but the Appian Way connected Rome with southern Italy and functioned as the western approach to this broader east-west network.