That the Roman Empire survived the seemingly mortal wound it had received at the era of the Great Interregnum, and continued to put forth pretensions which no one was likely to make good where the Hohenstaufen had failed, has been attributed to its identification with the German kingdom, in which some life was still left. But this was far from being the only cause which saved it from extinction. It had not ceased to be upheld in the fourteenth and fifteenth centuries by the same singular theory which had in the ninth and tenth been strong enough to re-establish it in the West. The character of that theory was indeed somewhat changed, for if not positively less religious, it was less exclusively so. In the days of Charles and Otto, the Empire, in so far as it was anything more than a tradition from times gone by, rested solely upon the belief that with the visible Church there must be coextensive a single Christian state under one head and governor. But now that the Emperor's headship had been repudiated by the Pope, and his interference in matters of religion denounced as a repetition of the sin of Uzziah; now that the memory of mutual injuries had kindled an unquenchable hatred between the champions of the ecclesiastical and those of the civil power, it was natural that the latter, while they urged, fervently as ever, the divine sanction given to the imperial office, should at the same time be led to seek some further basis whereon to establish its claims. What that basis was, and how they were guided to it, will best appear when a word or two has been said on the nature of the change that had passed on Europe in the course of the three preceding centuries, and the progress of the human mind during the same period. [Sidenote: Revival of learning and literature, A.D. 1100-1400.]