Mysia was ancient region in northwest Asia Minor, adjoining the Sea of Marmara on the north and the Aegean Sea on the west. Mysia was bounded by the teritories of Lydia on the south and Phrygia and Bithynia on the east. The District of Mysia is a geographical, rather than a political territory. Pergamon (Pergamum) and Kyzikos (Cyzicus) were its largest cities.
Homer mentioned the Mysians as ancient allies of the Trojans in Iliad.
In ancient times it was inhabited by the Mysi, by Aeolian Greeks, and by other groups. Mysia was ruled successively by Lydia, Persia, and Pergamon, and since 129 BC by Rome.
Alexander the Great's conquest of the Persian Empire (334-325 BC) freed the area, but its cities soon became the prey of contending Hellenistic monarchs. In the turbulent era following the death of Alexander (323 BC), Pergamon became the capital of a flourishing Hellenistic kingdom and one of the principal centers of Hellenistic civilization. It had formal autonomy under the Attalids, who, however, interfered in most aspects of civic government. Initially they ruled Pergamon as vassals of the Seleukid Kingdom, but Eumenes I declared himself independent of Antiochos I (263 BC). When he died in 241 BC, he was succeeded by his nephew Attalos I, who defeated the Galatians and assumed the royal title; the dynasty received its name from him.
The original Attalid territory around Pergamum was greatly expanded by 188 BC with the addition of Lydia, part of Phrygia, Lykaonia, and Pisidia (from 183 BC), all former Seleukid territories. This expansion was accomplished as the result of Eumenes II's alliance with Rome in its conflict with the Seleucid Antiochos III.
When Eumenes' son and second successor, Attalos III, died without an heir, he bequeathed the kingdom to Rome (133 BC). Rome accepted it and set up the province of Asia (129 BC), which included Ionia and the territory of Pergamon, but left the other regions to neighbouring kings, who were clients of Rome. The kingdom of Pergamon yielded much wealth, especially in agricultural surpluses and silver, first to the Attalid rulers and later to Rome.