\Galatia\ has been called the "Gallia" of the East, Roman writers calling its inhabitants Galli. They were an intermixture of Gauls and Greeks, and hence were called Gallo-Graeci, and the country Gallo-Graecia. The Galatians were in their origin a part of that great Celtic migration which invaded Macedonia about B.C. 280. They were invited by the king of Bithynia to cross over into Asia Minor to assist him in his wars. There they ultimately settled, and being strengthened by fresh accessions of the same clan from Europe, they overran Bithynia, and supported themselves by plundering neighbouring countries. They were great warriors, and hired themselves out as mercenary soldiers, sometimes fighting on both sides in the great battles of the times. They were at length brought under the power of Rome in B.C. 189, and Galatia became a Roman province B.C. 25.
This province of Galatia, within the limits of which these Celtic tribes were confined, was the central region of Asia Minor.
During his second missionary journey Paul, accompanied by Silas and Timothy (Acts 16:6), visited the "region of Galatia," where he was detained by sickness (Gal. 4:13), and had thus the longer opportunity of preaching to them the gospel. On his third journey he went over "all the country of Galatia and Phrygia in order" (Acts 18:23). Crescens was sent thither by Paul toward the close of his life (2 Tim. 4:10).
Initial text from Easton's Bible Dictionary, 1897 -- Please update as needed