The conquest of Naples was Lewis's special task and the practical object of his expedition to Rome. It would have infallibly constituted him ruler of Italy and have probably established the Minorite monk as pope in deserted S. Peter's. The Emperor was actively engaged with the scheme; but the absence of Castruccio, the dearth of means, and the procrastination of his allies prevented its fulfilment. King Robert, by sending his troops into the Campagna, challenged the Emperor to war immediately after the elevation of the anti-pope. His galleys pushed up the Tiber as far as S. Paul's; Lewis's forces were driven from Ostia, and these disasters produced the worst impression in the city.

On May 17 the Emperor went to Tivoli for four days only and merely with the ostentatious object of affording the Romans a pompous coronation spectacle. He returned on Whitsunday, spent the night at S. Lorenzo, caused himself to be received with great solemnity, and proceeded through the flower-decked city to S. Peter's. Here he placed the tiara on his Pope's head, the Pope the crown on his, so that one seemed to ratify the other. Lewis then revived the ban which Henry VII. had hurled against Robert; the anti-pope also pronounced the excommunication against John XXII., and commanded all who refused to recognise himself to appear before the Inquisition.