In 957 Cologne was constituted an imperial free city, having as its nominal prince the archbishop of the see, but possessing the right to govern its own affairs. The good bishop of that time acquiesced in the arrangement, but his successors were not content to be princes in name only, and strove hard to obtain a real influence over the citizens. Being for the most part men of unscrupulous disposition, they did not hesitate to rouse commonalty and aristocracy against each other, hoping to step in and reap the benefits of such internecine warfare as might ensue. And, indeed, the continual strife was not conducive to the prosperity of the burghers, but rather tended to sap their independence, and one by one their civil liberties were surrendered. Thus the scheming archbishops increased their power and influence in the city of Cologne. There came a time, however, in the civic history when the limit was overstepped. In the thirteenth century Archbishop Engelbert, more daring and ambitious than any of his predecessors, demanded that the municipal treasure should be given up to him. Not content with taking away the privileges of the burghers, he wished to lay his hands on the public purse as well. This was indeed the last straw, and the sluggish blood of the burghers was at length roused to revolt. At this time the Burgomaster of Cologne, Hermann Grein by name, was an honest, far-seeing, and diplomatic citizen, who had seen with dismay the ancient liberties of his beloved city destroyed by the cunning of the Archbishop. The latter's bold attempt at further encroachments gave him the opportunity he sought, and with the skill of a born leader Hermann Grein united nobles and commons in the determination to resist their mutual enemy. Feuds were for the time being forgotten, and with a gallant effort the galling yoke of the Archbishop-prince was thrown off, and the people of Cologne were once more free. Grein performed his civic duties so firmly, albeit so smoothly and gently, that he won the love and respect of all sections of the populace. Old and young hailed him in their hearts as the deliverer of their city from ecclesiastical tyranny. Only Engelbert hated him with a deadly hatred, and swore to be revenged; nor was his resolve weakened when a later attempt to subdue the city was frustrated by the foresight of Grein. It became obvious to the Archbishop that force was unavailing, for the majority of all classes were on the side of liberty, and were likely to remain so while Hermann Grein was at their head. So he made up his mind to accomplish by means of strategy the death of the good old man.