Human victims were also offered by way of thanksgiving after victory, and vows were often made before a battle, promising these as well as part of the spoil. For this reason the Celts would never ransom their captives, but offered them in sacrifice, animals captured being immolated along with them.[796] The method of sacrifice was slaughter by sword or spear, hanging, impaling, dismembering, and drowning. Some gods were propitiated by one particular mode of sacrifice--Taranis by burning, Teutates by suffocation, Esus (perhaps a tree-god) by hanging on a tree. Drowning meant devoting the victim to water-divinities.[797] Other propitiatory sacrifices took place at intervals, and had a general or tribal character, the victims being criminals or slaves or even members of the tribe. The sacrificial pile had the rude outline of a human form, the limbs of osier, enclosing human as well as some animal victims, who perished by fire. Diodorus says that the victims were malefactors who had been kept in prison for five years, and that some of them were impaled.[798] This need not mean that the holocausts were quinquennial, for they may have been offered yearly, at Midsummer, to judge by the ritual of modern survivals.[799] The victims perished in that element by which the sun-god chiefly manifested himself, and by the sacrifice his powers were augmented, and thus growth and fertility were promoted. These holocausts were probably extensions of an earlier slaying of a victim representing the spirit of vegetation, though their value in aiding fertility would be still in evidence. This is suggested by Strabo's words that the greater the number of murders the greater would be the fertility of the land, probably meaning that there would then be more criminals as sacrificial victims.[800] Varro also speaks of human sacrifice to a god equated with Saturn, offered because of all seeds the human race is the best, i.e. human victims are most productive of fertility.[801] Thus, looked at in one way, the later rite was a propitiatory sacrifice, in another it was an act of magico-religious ritual springing from the old rite of the divine victim. But from both points of view the intention was the same--the promotion of fertility in field and fold. Divination with the bodies of human victims is attested by Tacitus, who says that "the Druids consult the gods in the palpitating entrails of men," and by Strabo, who describes the striking down of the victim by the sword and the predicting of the future from his convulsive movements.[802] To this we shall return.