Gregory did not lose his courage even with the enemy at his gate. The Romans were faithful to him, and Henry, who saw no chance of besieging the great city successfully, was forced to retreat northwards by the feverish heat of summer. [Sidenote: War between Henry and Gregory, 1081–1084.] He retired to Lombardy, where his position was unassailable. Next year he was back again before the walls of Rome, but the occupation of Tivoli was his greatest success. In 1083 a third attack gave him possession of the Leonine city, but even in this extremity Gregory would listen to no talk of conciliation. ‘Let the king lay down his crown and make atonement to the Church,’ was his answer to those who besought him to come to terms. In the early months of 1084 Henry invaded Apulia and kept in check the Normans, who at last were making a show of helping the Pope. In March he appeared for the fourth time before Rome. This time the Romans opened their gates, and Gregory was closely besieged in the castle of St. Angelo. [Sidenote: Coronation of Henry by Guibert, 1084.] A synod was hastily summoned, which renewed his deposition and excommunication. On Palm Sunday, 1084, Guibert was enthroned, and on Easter Day he crowned Henry Emperor at St. Peter’s. [Sidenote: The Normans come to Gregory’s help, 1084.] Gregory sent from the castle of St. Angelo an urgent appeal for help to Robert Guiscard. During the troubles of the last few years, Robert’s obligations to his suzerain had weighed very lightly upon him, but Henry’s invasion of Apulia and the certain ruin of the Normans in Naples if the Pope succumbed, at last brought him to decided action. Hastily abandoning his Greek campaign, Robert crossed over to Italy, and in May advanced to the walls of Rome with a large and motley army, in which the Saracens of Sicily were a prominent element. Henry, who had no force sufficient to resist, quitted Rome, and soon crossed the Alps. The Romans tried in vain to defend their city from the Normans. After a four days’ siege treason opened the gates. [Sidenote: Sack of Rome.] Rome was ruthlessly sacked, whole quarters were burned down, hideous massacres and outrages were perpetrated, and thousands of Romans were sold as slaves. The Normans then marched home. Gregory could not remain in the desolate city, and followed them to Salerno. The Antipope kept his Christmas amid the ruins of Rome, but soon abandoned the city for his old home at Ravenna. Gregory now fell sick at Salerno. The few faithful cardinals strove to console him by dwelling on the great work which he had accomplished. [Sidenote: Death of Gregory in exile, 1085.] ‘I set no store by what I have done,’ was his answer. ‘One thing only fills me with hope. I have always loved the law of God and hated iniquity. Therefore I die in exile.’ He passed away on 25th May 1085. Less than two months afterwards, Robert Guiscard died at Corfu.