That period in modern history at which the deliberative oath had assumed something of its ultimate shape is marked by the occurrence of one singular invasion of its solemnity. The incident we refer to is the charge preferred by Thomas-a-Becket against John the Marshal, to the effect that he had sworn upon a "book of old songs" instead of upon the sacred writings which had then become the proper instruments for this purpose. Indeed, in tracing the history of these observances it would seem as if an endeavour was being constantly made to frustrate the aims and ends of swearing, and that the more Christian modes were only resorted to when every pagan method had been found inoperative. To swear upon the authority of everything that was terrible or grotesque--by the sword or javelin of a conquering nation, as by the love-token on a maiden's sleeve;[1] by the sepulchre of a debtor;[2] by the abbey church at Glastonbury,[3] or by the price of the potter's field[4]--these were expedients that had been tried and been forsaken before the modern forms of swearing were reached. Like the time-expired worship of the divinities of the mythology that, in the one solitary temple of Mount Casano, was maintained for some hundred years after the gods of Olympus had been deposed: so the impious oaths of pagandom continued to jostle and wrestle with those of Christianity for many centuries after authority had pronounced their doom. "Olympian Jupiter!" exclaims Aristophanes, at the mention of that oath, "to think of your believing in Jupiter, as old as you are!" How stubbornly the ground was contested may be inferred from the enactments of civil and ecclesiastical law. So early as the ninth century, Justinian prescribed the punishment of death for the offence of swearing by the limbs of God. The code that prevailed in the northern districts of Britain was more severe than any that was enforced elsewhere in these islands. By statutes of Donald VI. and Kenneth II., the penalty of cutting out the tongue was inflicted upon swearers. In France, Charlemagne legislated expressly against the practice of impious oath-taking, and by an edict of Philip II. swearers were condemned to drowning in the Seine.[5] The Council of Constantinople passed a sentence of excommunication upon the swearers of heathen oaths.