The Celts were an ancient people who migrated to Europe centuries before the time of Christ. They inhabited Galatia, Gaul, Britain, and Ireland, among other places.
The Scythians, the Celts, the Iberians, and the Thracians—all of them are warlike races. And they are greatly addicted to intoxication, thinking that it is an honorable, happy pursuit to engage in. Clement of Alexandria (c. 195, E), 2.245, 246.
The Nasamones consult private oracles by frequent and lengthened visits to the sepulchers of their relatives. . . . And the Celts, for the same purpose, stay all night at the tombs of their brave chieftains. Tertullian (c. 210, W), 3.234.
It is plain that the province was called Galatia from the following circumstances: Upon their arrival in [the region], the Gauls [i.e., Celts] united themselves with the Greeks. Because of that, the region was called Gallogrecia, and later, Galatia. It is no wonder if he said those things concerning the Galatians and related how a people of the West traveled over so great a distance in the middle of the earth and settled in a region of the East. Lactantius (c. 304–313, W), 7.323.