By an effective piece of audacity, that of sporting the imperial flag and the Burgundian cross, Franz spread abroad the idea that he was acting on behalf of the Emperor, then absent in Spain; and this largely contributed to the result that his army speedily rose to 5000 knights and 10,000 footmen. The Imperial Diet at Nürnberg now intervened, and ordered Sickingen to cease the operations he had already begun, threatening him with the ban of the Empire and a fine of 2000 marks if he did not obey. To this summons Franz sent a characteristically impudent reply,[21] and light-heartedly continued the campaign, regardless of the warning which an astrologer had given him some time previously, that the year 1522 or 1523 would probably be fatal to him. It is evident that this campaign, begun so late in the year, was regarded by Sickingen and the other leaders as merely a preliminary canter to a larger and more widespread movement the following spring, since on this occasion the Swabian and Franconian knighthood do not appear to have been even invited to take part in it. After an easy progress, during which several trifling places, the most important being St. Wendel, were taken, Franz with his army arrived on the 8th of September before the gates of Trier. He had hoped to capture the town by surprise, and was indeed not without some expectation of co-operation and help from the citizens themselves. On his arrival he shot letters within the walls summoning the inhabitants to take his part against their tyrant; but either through the unwillingness of the burghers to act with the knights, or through the vigilance of the archbishop, they were without effect. The gates remained closed; and in answer to Sickingen's summons to surrender, Richard replied that he would find him in the city if he could get inside. In the meantime Sickingen's friends had signally failed in their attempts to obtain supplies and reinforcements for him, in the main owing to the energetic action of some of the higher nobles. The Archbishop of Trier showed himself as much a soldier as a churchman; and after a week's siege, during which Sickingen made five assaults on the city, his powder ran out, and he was forced to retire. He at once made his way back to Ebernburg, where he intended to pass the winter, since he saw that it was useless to continue the campaign, with his own army diminishing and the hoped-for supplies not appearing, whilst the forces of his antagonists augmented daily. In his stronghold of Ebernburg he could rely on being secure from all attack until he was able to again take the field on the offensive, as he anticipated doing in the spring.