de bello gallico, 6.16

The nation of all the Gauls is exceedingly devoted to religious rites, and because of this reason (those) who have been afflicted with more severe diseases and who are engaged in battles and dangers either sacrifice men as victims or vow that they will sacrifice them and use the Druids as ministers for those sacrifices; because they think that, unless the life of a man be returned for the life of a man, the will of the immortal gods can not be propitiated, and they have sacrifices of the same kind established publicly. Others have figures of immense size, the limbs of which woven with twigs they fill with living men; with which having been set on fire, the men perish surrounded by flame. They think that the punishment of such who have been taken in theft, or in robbery, or in any offense, is more pleasing to the immortal gods, but, when a supply of that type is lacking, they descend to the punishment of the innocent.