A more pressing duty suspended the prosecution of his ambitious designs. By shipwreck, pestilence, and the sword his army was reduced to a third of the original numbers; and instead of being recruited from Italy, he was informed, by plaintive epistles, of the mischiefs and dangers which had been produced by his absence; the revolt of the cities and barons of Apulia, the distress of the pope, and the approach or invasion of Henry, king of Germany. Highly presuming that his person was sufficient for the public safety, he repassed the sea in a single brigantine, and left the remains of the army under the command of his son and the Norman counts, exhorting Bohemond to respect the freedom of his peers, and the counts to obey the authority of their leader. The son of Guiscard trod in the footsteps of his father; and the two destroyers are compared, by the Greeks, to the caterpillar and the locust, the last of whom devours whatever has escaped the teeth of the former. After winning two battles against the emperor, he descended into the plain of Thessaly, and besieged Larissa, the fabulous realm of Achilles, which contained the treasure and magazines of the Byzantine camp. The courage of Bohemond was always conspicuous, and often successful; but his camp was pillaged by a stratagem of the Greeks; the city was impregnable; and the venal or discontented counts deserted his standard, betrayed their trusts, and enlisted in the service of the emperor. Alexius returned to Constantinople with the advantage, rather than the honour, of victory. After evacuating the conquests which he could no longer defend, the son of Guiscard embarked for Italy, and was embraced by a father who esteemed his merit, and sympathised in his misfortune. Of the Latin princes, the allies of Alexius and enemies of Robert, the most prompt and powerful was Henry IV, king of Germany and Italy, and future emperor of the West. Henry was the severe adversary of the Normans, the allies and vassals of Gregory VII, his implacable foe. The long quarrel of the throne and mitre had been recently kindled by the zeal and ambition of that haughty priest; the king and the pope had degraded each other, and each had seated a rival on the temporal or spiritual throne of his antagonist. After the defeat and death of his Swabian rebel, Henry descended into Italy, to assume the imperial crown, and to drive from the Vatican the tyrant of the church. But the Roman people adhered to the cause of Gregory; their resolution was fortified by supplies of men and money from Apulia; and the city was thrice ineffectually besieged by the king of Germany.