Cassius and Brutus, having usurped control of most of the Eastern provinces, including Macedonia, Asia Minor, and Syria, combine their armies, cross the Hellespont, march through Thrace, and encamp near Philippi (near present Kavalla) in Macedonia.

The combined armies, with forces roughly equal those of their opponents, lie astride the Via Egnatia to the west of Philippi, their position being partly protected by a marsh.

Their intention is to starve out the enemy, but they are forced into an engagement.

Brutus is successful against Octavian's camp, but Cassius, defeated by Antony's successful attack on the camp, gives up all for lost and orders his freedman Pindarus to slay him.

He is mourned by Brutus as "the Last of the Romans" and buried at Thasos.

Brutus, against his better judgment, fights a second action about three weeks later, on October 23, in which he is routed; despairing of restoring the republican cause, he too commits suicide, leaving the triumvirate in control of the Roman Republic.

Plutarch reports that Antony covered Brutus' body with a purple garment as a sign of respect: they had been friends.

He remembered that Brutus had placed as a condition for his joining the plot to assassinate Caesar that the life of Antony should be spared.

Many other young Roman aristocrats lost their life in the battle or committed suicide after the defeat, including the son of great orator Hortensius, and Marcus Porcius Cato (II) (the son of Cato the younger), and Marcus Livius Drusus Claudianus (the father of Livia, who became Octavian’s wife).

Porcia, Brutus’ wife, reportedly also killed herself by swallowing a red-hot coal when she received news of the defeat. (According to Plutarch [Brutus 53 para 2], there is some dispute as to whether this is the case: Plutarch states that there is a letter in existence that was allegedly written by Brutus mourning the manner of her death.)

Some of the nobles who are able to escape negotiate their surrender to Antony and enter his service (among them Marcus Calpurnius Bibulus and Marcus Valerius Messalla Corvinus).

Apparently, the nobles do not want to deal with the young and merciless Octavian. (Mark Antony will later use the examples of these battles as a means to belittle Octavian, as both battles had been decisively won with the use of Antony's forces.

In addition to claiming responsibility for both victories, Antony will also brand Octavian as a coward for handing over his direct military control to his boyhood friend, Marcus Vipsanius Agrippa, instead.)

Sextus Pompeius in 44 following the assassination of Caesar had come to terms with Mark Antony and been given a naval command, but in August 43 he had been outlawed.

Despite the fact the Sextus is controlling Sicily and Domitius Ahenobarbus still commands the republican fleet, the republican resistance had been definitely crushed at Philippi.

The remains of the Liberators’ army are rounded up and roughly fourteen thousand men are enrolled into the triumvirs’ army.

Old veterans are discharged back to Italy, but some of the veterans remain in the town of Philippi, which becomes a Roman colony (this will later be reinforced by Augustus).

After the battle, a new arrangement is made between the members of the Second Triumvirate, who agree to divide the empire.

Antony proceeds to take up the administration of the eastern provinces.

Mark Antony and Octavian are heirs to the military-political organization built by the murdered dictator Julius Caesar.

Rome’s ruling body, the triumvirate, consisting of Octavian, Antony, and Marcus Aemilius Lepidus, had expired on the last day of 33 BCE; it is not renewed.

Another civil war is beginning.

A propaganda war is fought during 33 and 32 BCE in the political arena of Rome, with accusations flying between sides.

Antony, residing in Egypt with Queen Cleopatra VII, divorces Octavia and accuses Octavian of being a social upstart, of usurping power, and of forging the adoption papers by Caesar.

Octavian responds with treason charges: of illegally keeping provinces that should be given to other men by lots, as is Rome's tradition, and of starting wars against foreign nations (Armenia and Parthia) without the consent of the Senate.

Antony is also held responsible for Sextus Pompeius' execution with no trial.

The Senate in 32 BCE deprives him of his prospective consulate for the following year and declares war against Cleopatra—not Antony, because Octavian has no wish to advertise his role in perpetuating Rome's internecine bloodshed.

Both sides mobilize in 32 for war on land and sea.

Both consuls, Gnaeus Domitius Ahenobarbus and Gaius Sosius, and a third of the Senate, abandon Rome to meet Antony and Cleopatra in Ephesus, to which the couple in the winter of 32—31 sail their newly assembled army and fleet.

The consuls Ahenobarbus and Sosius, having departed Rome for Antony’s headquarters, have brought with them numerous Roman senators, probably more than two hundred.

Ahenobarbus, finding Cleopatra with Antony, endeavors, in vain, to obtain her removal from the army.

Antony moves his headquarters at the beginning of 31 BCE from Ephesus to Athens and …

Antony moves his headquarters from Athens to Patras.

As he loses more ground, the morale of his advisers and fighting forces deteriorates, a process aided by Cleopatra's insistence on being present at his headquarters against the wishes of many of his leading Roman supporters, thus providing Octavian with fresh propaganda fuel.

Because of this lack of unity and the inexperience of Antony's crews, the decisive battle is lost before it ever begins.

With five hundred ships and seventy thousand infantry, Antony makes his camp at Actium, which lies on the southern side of a strait leading from the Ionian Sea into the Ambracian Gulf.

Octavian, with four hundred ships and eighty thousand infantry, arrives from the north and, by occupying Patrae and Corinth, manages to cut Antony's southward communications with Egypt via the Peloponnese.

Antony's army is trapped on land and sea. Deserters flee to Octavian's side daily while Octavian's forces are comfortable enough to make preparations.

Many of the soldiers, disgusted with Antony’s conduct, offer the command to the consul Ahenobarbus, but he prefers to desert the party altogether, and defects to Octavian shortly before the Battle of Actium.

Suffering from a fever, he takes a small boat to Octavian's side.

Antony is greatly upset by this defection, but he nevertheless sends Ahenobarbus him all his gear, his friends and his attendants.

Ahenobarbus is not, however, present at the battle itself, as he dies a few days after joining Augustus.

Plutarch suggests that his death was due to "the shame of his disloyalty and treachery being exposed."

Suetonius says that he was the best of his family.

Desertions by some of his allies and a lack of provisions soon force Antony on September 2, 31 BCE to take action.

Either hoping to win at sea because he is outmaneuvered on land or making a desperate attempt to break free of the naval blockade, he draws up his ships outside the bay, facing west, with Cleopatra's squadron behind.

Sailing his fleet through the bay of Actium on the western coast of Greece, Antony fleet faces the much larger fleet of smaller, more maneuverable ships under commanders Agrippa and Gaius Sosius.

In the ensuing naval contest, each side's squadrons try to outflank the other until Cleopatra, by prearranged plan rather than treachery, takes her sixty Egyptian galleys (carrying her and Antony's treasury) and flees the battle.

Antony then breaks off and with a few ships manages to follow her.

The remainder of his fleet becomes disheartened and surrenders to Octavian; Antony's land forces surrender one week later.

Octavian has previously shown little mercy to military combatants and acted in ways that have proven unpopular with the Roman people, yet he is given credit for pardoning many of his opponents after the Battle of Actium.