H. 4.--Caesar further tells us that the Druids taught the doctrine of transmigration of souls, and that their course of education included astronomy, geography, physics, and theology. The attributes of their chief God corresponded, in his view, with those of the Roman Mercury. Of the minor divinities, one, like Apollo, was the patron of healing; a second, like Minerva, presided over craft-work; a third, like Jupiter, was King of Heaven, and a fourth, like Mars, was the War-god.[55] Their calendar was constructed on the principle that each night belongs to the day before it (not to that after it, as was the theory amongst the Mediterranean nations), and they reckoned all periods of time by nights, not days, as we still do in the word "fortnight." For this practice they gave the mystical reason that the Celtic races were the Children of Darkness. At periods of national or private distress, human sacrifices were in vogue amongst them, sometimes on a vast scale. "They have images [_simulacra_] of huge size, whose limbs when enclosed [_contexta_] with wattles, they fill with living men. The wattles are fired and the men perish amid the hedge of flame [_circumventi flamma exanimantur homines_]." It is usually supposed that these _simulacra_ were hollow idols of basket-work. But such would require to be constructed on an incredible scale for their limbs to be filled with men; and it is much more probable that they were spaces traced out upon the ground (like the Giant on the hill above Cerne Abbas in Dorset), and hedged in with the wattles to be fired. H. 5.--From the historian Diodorus Siculus, whose life overlapped Caesar's, we learn that Druid was a native British name. "There are certain philosophers and theologians held in great honour whom they call Druids."[56] Whether this designation is actually of Celtic derivation is, however, uncertain. Pliny thought it was from the Greek affected by the Druids and connected with their oak-tree worship. Professor Rhys mentions that the earliest use of the word in extant Welsh literature is in the Book of Taliesin, under the form _Derwyddon_,[57] and that in Irish is to be found the cognate form _Drui_. But these are as likely to be derived from the Greek [Greek: _drouides_] as this from them. Diodorus adds that they have mighty influence, and preside at all sacred rites, "as possessing special knowledge of the Gods, yea, and being of one speech [[Greek: homophônôn]] with them." This points to some archaic or foreign language, possibly Greek, being used in the Druidical ritual. Their influence, he goes on to say, always makes for peace: "Oft-times, when hosts be arrayed, and either side charging the one against the other, yea, when swords are out and spears couched for the onset, will these men rush between and stay the warriors, charming them to rest [[Greek: katepasantes]] like so many wild beasts."