Antony, with Octavia, returned to the East, where he found that his legate Ventidius had gained the most brilliant success over the Parthians. This man was a native of Picenum, and originally a mule-driver. He was taken prisoner in the Social War, and walked in chains in the triumphal procession of Pompeius Strato. He was made Tribune of the Plebs by Julius Cæsar, and was raised to the Consulship in B.C. 43. In the Parthian War he displayed military abilities of no ordinary kind. He first defeated Labienus, took him prisoner in Cilicia, and put him to death. He then entered Syria, and drove Pacorus beyond the Euphrates. In the following year (B.C. 38) the Parthians again entered Syria, but Ventidius gained a signal victory over them, and Pacorus himself fell in the battle.

The treaty between Sextus Pompey and the Triumvirs did not last long. Antony refused to give up Achaia, and Pompey therefore recommenced his piratical excursions. The price of provisions at Rome immediately rose, and Octavian found it necessary to commence war immediately; but his fleet was twice defeated by Pompey, and was at last completely destroyed by a storm (B.C. 38). This failure only proved the necessity of making still more extensive preparations to carry on the war with success. The power of Octavian was insecure as long as Pompey was master of the sea, and could deprive Rome of her supplies of corn. Nearly two years were spent in building a new fleet, and exercising the newly-raised crews and rowers. The command of the fleet and the superintendence of all the necessary preparations for the war were intrusted to Agrippa. In order to obtain a perfectly secure and land-locked basin for his fleet, and thus secure it against any sudden surprise, he constructed the celebrated Julius Portus on the coast of Campania, near Baiæ, by connecting the inland Lake Avernus, by means of a canal, with the Lake Lucrinus, and by strengthening the latter lake against the sea, by an artificial dike or dam. While he was engaged in these great works, Antony sailed to Taventum, in B.C. 37, with 300 ships. Mæcenas hastened thither from Rome, and succeeded once more in concluding an amicable arrangement. He was accompanied on this occasion by Horace, who has immortalized, in a well-known satire, his journey from Rome to Brundusium. Octavian and Antony met between Tarentum and Metapontum; the Triumvirate was renewed for another period of five years; Antony agreed to leave 120 ships to assist in the war against Pompey, and Octavian promised to send a land force to the East for the campaign against the Parthians.

Octavian, now relieved of all anxiety on the part of Antony, urged on his preparations with redoubled vigor. By the summer of B.C. 36 he was ready to commence operations. He had three large fleets at his disposal: his own, stationed in the Julian harbor; that of Antony, under the command of Statilius Taurus, in the harbor of Tarentum; and that of Lepidus, off the coast of Africa. His plan was for all three fleets to set sail on the same day, and make a descent upon three different parts of Sicily; but a fearful storm marred this project. Lepidus alone reached the coast of Sicily, and landed at Lilybæum; Statilius Taurus was able to put back to Tarentum; but Octavian, who was surprised by the storm off the Lucanian promontory of Palinurus, lost a great number of his ships, and was obliged to remain in Italy to repair his shattered fleet. As soon as the ships had been refitted, Octavian again set sail for Sicily. Agrippa defeated Pompey's fleet off Mylæ, destroying 30 of his ships; but the decisive battle was fought on the 3d of September (B.C. 36), off Naulochus, a sea-port between Mylæ and the promontory of Pelorus. Agrippa gained a brilliant victory; most of the Pompeian vessels were destroyed or taken. Pompey himself fled to Lesbos with a squadron of 17 ships. Octavian did not pursue him, as Lepidus, who was at the head of a considerable force, now claimed Sicily for himself, and an equal share as Triumvir in the government of the Roman world; but Octavian found means to seduce his soldiers from their allegiance; and Lepidus was at last obliged to surrender to Octavian, and to throw himself upon his mercy. His life was granted, but he was deprived of his Triumvirate, his army, and his provinces, and was compelled to retire to Italy as a private person. He was allowed, however, to retain his property and the dignity of Pontifex Maximus. He lived till B.C. 13.

In B.C. 35 Pompey crossed over from Lesbos to Asia, with the view of seizing that province; but he was easily crushed by the lieutenants of Antony, was taken prisoner as he attempted to escape to Armenia, and was put to death at Miletus. By the death of Pompey and the deposition of Lepidus, Antony and Octavian were now left without a rival, and Antony's mad love for Cleopatra soon made Octavian the undisputed master of the Roman world.

After Antony's marriage with Octavia in B.C. 40, he seems for a time to have forgotten, or, at least, conquered the fascinations of the Egyptian queen. For the next three years he resided in Athens with his wife; but after his visit to Italy, and the renewal of the Triumvirate in B.C. 37, he left Octavia behind at Tarentum, and determined to carry out his long-projected campaign against the Parthians. As he approached Syria, "that great evil," as Plutarch calls it, his passion for Cleopatra, burst forth with more vehemence than ever. From this time she appears as his evil genius. He summoned her to him at Laodicea, and loaded her with honors and favors. He added to her dominions Phœnicia, Cœle-Syria, Cyprus, a large part of Cilicia, Palestine, and Arabia, and publicly recognized the children she had borne him. Although he had collected a large army to invade the Parthian empire, he was unable to tear himself away from the enchantress, and did not commence his march till late in the year. The expedition proved most disastrous; the army suffered from want of provisions, and Antony found himself compelled to retreat. He narrowly escaped the fate of Crassus, and it was with the utmost difficulty that he succeeded in reaching the Armenian mountains, after losing the best part of his troops.

Antony returned to Alexandria, and surrendered himself entirely to Cleopatra. In B.C. 34 he made a short campaign into Armenia, and succeeded in obtaining possession of Artavasdas, the Armenian king. He carried him to Alexandria, and, to the great scandal of all the Romans, entered the city in triumph, with all the pomp and ceremonial of the Roman pageant. He now laid aside entirely the character of a Roman citizen, and assumed the state and dress of an Eastern monarch. Instead of the toga he wore a robe of purple, and his head was crowned with a diadem. Sometimes he assumed the character of Osiris, while Cleopatra appeared at his side as Isis. He gave the title of kings to Alexander and Ptolemy, his sons by Cleopatra. The Egyptian queen already dreamed of reigning over the Roman world.

While Antony was disgusting the Romans and alienating his friends and supporters by his senseless follies, Octavian had been restoring order to Italy, and, by his wise and energetic administration, was slowly repairing the evils of the civil wars. In order to give security to the frontiers and employment to the troops, he attacked the barbarians on the north of Italy and Greece, and subdued the Iapydes, Pannonians, and Dalmatians. He carried on these wars in person, and won the affection of the soldiers by sharing their dangers and hardships.

The contrast between the two Triumvirs was sufficiently striking, but Octavian called attention to the follies of Antony. Letters passed between them full of mutual recriminations, and both parties began to prepare for the inevitable struggle. Toward the end of B.C. 32 the Senate declared war against Cleopatra, for Antony was regarded as her slave.[72] The five years of the Triumvirate had expired on the last day of this year; and on the 1st of January, B.C. 31, Octavian, as Consul of the Republic, proceeded to carry on the war against the Egyptian queen. The hostile fleets and armies assembled on the western coasts of Greece. Antony's fleet was superior both in number and size of the ships, but they were clumsy and unmanageable. They were anchored in the Ambraciot Gulf, in the modern Bay of Prevesa. (See Plan, P.) The army was encamped on the promontory of Actium (Plan, 3), which has given its name to the battle. The fleet of Octavian consisted of light Liburnian vessels, manned by crews which had gained experience in the wars against Sextus Pompey. It was under the command of the able Agrippa, who took up his station at Corcyra, and swept the Adriatic Sea. Octavian in person took the command of the land forces, which were encamped on the coast of Epirus opposite Actium, on the spot where Nicopolis afterward stood. (Plan, 1.) The generals of Antony strongly urged him to fight on land; but the desertions among his troops were numerous; Cleopatra became alarmed for her safety; and it was therefore resolved to sacrifice the army, and retire with the fleet to Egypt. But Agrippa was on the watch, and Antony had no sooner sailed outside the strait than he was compelled to fight. The battle was still undecided and equally favorable to both parties, when Cleopatra, whose vessels were at anchor in the rear, taking advantage of a favorable breeze which sprang up, sailed through the midst of the combatants with her squadron of 60 ships, and made for the coast of Peloponnesus. When Antony saw her flight, he hastily followed her, forgetting every thing else, and shamefully deserting those who were fighting and dying in his cause. The remainder of the fleet was destroyed before night-time. The army, after a few days' hesitation, surrendered, and Octavian pardoned all the officers who sued for his favor. The battle of Actium was fought on the 2d of September, B.C. 31, from which day the reign of Octavian is to be dated.

Octavian did not follow Antony to Alexandria for nearly twelve months after the battle of Actium. He sent Agrippa to Italy with his veteran troops, and himself passed the winter at Samos; but he could not satisfy the demands of the soldiers, who broke out into open mutiny. Octavian hastened to Brundusium, and with difficulty raised a sufficient sum of money to calm their discontent.