Ancient and modern region of the southeastern Balkans; in ancient times, the part north of Greek settlement extending to the Black Sea. In the 5th century BC, it included modern Bulgaria and Romania. Most Thracians became subject to Persia in c 516-510 BC. It was assimilated (356-342 BC) by Philip II of Macedon and later provided Philip's son, Alexander the Great, with troops during his conquests. In 197 BC, Rome assigned much of Thrace to the kingdom of Pergamum. In the 1st century BC, Rome became more involved in the affairs of the region and emperor Claudius I annexed the entire Thracian kingdom in 46 AD. Thrace was subsequently made into a Roman province. The emperor Trajan and his successor, Hadrian, founded cities in Thrace, notably Sardica (modern Sofia) and Hadrianopolis (modern Edirne). In about 300 AD, Diocletian reorganized the area between the Lower Danube and the Aegean into the diocese of Thrace. Archaeological sites are the homes of Democritus, the 5th-century philosopher, and of Protagoras, a counselor of Alexander the Great; and the Roman highway Via Egnatia.