Several of these instances have shown the use of spells, and the Druid was believed to possess powerful incantations to discomfit an enemy or to produce other magical results. A special posture was adopted--standing on one leg, with one arm outstretched and one eye closed, perhaps to concentrate the force of the spell,[1122] but the power lay mainly in the spoken words, as we have seen in discussing Celtic formulæ of prayer. Such spells were also used by the _Filid_, or poets, since most primitive poetry has a magical aspect. Part of the training of the bard consisted in learning traditional incantations, which, used with due ritual, produced the magic result.[1123] Some of these incantations have already come before our notice, and probably some of the verses which Cæsar says the Druids would not commit to writing were of the nature of spells.[1124] The virtue of the spell lay in the spoken formula, usually introducing the name of a god or spirit, later a saint, in order to procure his intervention, through the power inherent in the name. Other charms recount an effect already produced, and this, through mimetic magic, is supposed to cause its repetition. The earliest written documents bearing upon the paganism of the insular Celts contain an appeal to "the science of Goibniu" to preserve butter, and another, for magical healing, runs, "I admire the healing which Diancecht left in his family, in order to bring health to those he succoured." These are found in an eighth or ninth century MS., and, with their appeal to pagan gods, were evidently used in Christian times.[1125] Most Druidic magic was accompanied by a spell-- transformation, invisibility, power over the elements, and the discovery of hidden persons or things. In other cases spells were used in medicine or for healing wounds. Thus the Tuatha Dé Danann told the Fomorians that they need not oppose them, because their Druids would restore the slain to life, and when Cúchulainn was wounded we hear less of medicines than of incantations used to stanch his blood.[1126] In other cases the Druid could remove barrenness by spells.