§-Syllabus dot point

NSWAncient HistorySyllabus dot point

How did the great civil war of 49 to 45 BC destroy the Roman Republic in practice and leave Caesar the master of the Roman world?

The civil war 49 to 45 BC, Caesar's seizure of Italy and Pompey's withdrawal to Greece, the Spanish campaign at Ilerda, the decisive battle of Pharsalus (48 BC) and Pompey's murder in Egypt, the Alexandrian War and Cleopatra, the defeat of the Pompeians and optimates at Zela (47 BC), Thapsus (46 BC) and Munda (45 BC), Caesar's accumulating dictatorships and clementia, and the replacement of the Republic in practice by the rule of one man

How the great civil war of 49 to 45 BC ended the Roman Republic in practice - Caesar's seizure of Italy, Pompey's withdrawal to Greece and defeat at Pharsalus, his murder in Egypt, and the mopping-up at Zela, Thapsus and Munda that left Caesar master of the Roman world through clementia and accumulating dictatorships.

Generated by Claude Opus 4.813 min answerUpdated 2026-07-01

Reviewed by: AI editorial process; not yet individually human-reviewed

Have a quick question? Jump to the Q&A page

Quick answer

The civil war of 49 to 45 BC ended the Roman Republic in practice. Caesar crossed the Rubicon on 10 January 49 BC and seized Italy in about sixty days; Pompey withdrew to Greece. After securing Spain at Ilerda (49 BC), Caesar recovered from a setback at Dyrrhachium to destroy Pompey's main army at Pharsalus on 9 August 48 BC; Pompey fled to Egypt and was murdered on 28 September 48 BC. The Alexandrian War drew Caesar into installing Cleopatra, and he crushed Pharnaces at Zela (47 BC, "veni, vidi, vici"). Organised resistance ended only at Thapsus (46 BC, with Cato's suicide at Utica) and Munda (45 BC). Caesar's dictatorships escalated from eleven days to ten years, and his policy of clementia bound pardoned enemies to his personal grace, so that by 45 BC the Republic survived in form but had become the rule of one man. Syme, Gruen and Meier debate whether the war itself or a longer decline was decisive.

Jump to a section

What this dot point is asking
The answer
How to read a source on this topic
Historians and the evidence base

What this dot point is asking

Within the period option "The fall of the Roman Republic 78 to 42 BC," this slice asks you to explain HOW the great civil war of 49 to 45 BC destroyed the Republic in practice and left Caesar the master of the Roman world. You need to trace the campaigns in order, Caesar's lightning seizure of Italy and Pompey's withdrawal to Greece, the Spanish campaign at Ilerda, the decisive battle of Pharsalus and Pompey's murder in Egypt, the Alexandrian War and Cleopatra, and the mopping-up of the Pompeians and optimates at Zela, Thapsus (with Cato's suicide at Utica) and Munda, and then to ARGUE about their significance: how Caesar's accumulating dictatorships and his policy of clementia turned a military victory into permanent one-man rule. As a Historical Period dot point it is examined mainly by essay, so the chronology is the raw material for an argument about change, causation and significance, not a story to retell.

In plain English

Imagine a country where power is meant to be shared by an elected council, and no one is allowed to bring an army into the capital. One popular general, told to disband his troops, instead marches them across the border, and once that line is crossed there is no going back. He grabs the capital before his rival can react, chases that rival overseas, and beats him in one enormous battle. The rival flees abroad and is murdered by people hoping to please the winner. Over the next three years the general hunts down the last of his opponents in Spain, Africa and the Middle East until nobody is left to say no to him. He is careful never to call himself "king" and even spares many of his enemies, but he keeps voting himself longer and longer terms as sole leader, until in practice the old council still meets but only ever agrees with him. The rules of the old system are still on the wall, but everyone knows they now mean whatever one man says. That is Rome between 49 and 45 BC.

The answer

The seizure of Italy and Pompey's withdrawal, 49 BC

The civil war began the moment Caesar led the Thirteenth Legion across the Rubicon on 10 January 49 BC, defying the Senate's demand that he disband his army. His opening moves were fast and, by his own account in the Commentarii de Bello Civili, almost bloodless. Rather than wait to be attacked, he drove south through Italy so quickly that town after town opened its gates. Pompey, who had boasted he needed only to stamp his foot for legions to spring up but in fact had few trained troops in Italy, judged the peninsula indefensible. He withdrew to Brundisium and, after Caesar failed to trap him there, crossed the Adriatic to Greece in March 49 BC with much of the Senate, intending to use his naval superiority and the wealth of the eastern provinces to build an army at leisure. Within roughly sixty days Caesar held all of Italy without a major battle, seizing the political centre of the Republic before his enemies could organise.

Ilerda and the securing of the west

Rather than pursue Pompey at once, Caesar first secured his rear. Pompey's legates Lucius Afranius and Marcus Petreius commanded seven veteran legions in Spain that could otherwise have struck at Italy behind him. In a campaign won largely through manoeuvre and the cutting of supply lines rather than pitched battle, Caesar forced their surrender at Ilerda in the summer of 49 BC, while the port of Massilia, which had sided with Pompey, fell after a siege later that year. Caesar later boasted that Spain had been won "without a battle" (Bellum Civile 1.72), a self-serving claim historians treat with caution but which broadly fits the manoeuvre-heavy campaign described. Named dictator briefly at the end of 49 BC to hold the elections, he then crossed to Greece to confront Pompey directly.

Pharsalus, 48 BC, and the death of Pompey

An initial defeat at Dyrrhachium in July 48 BC, where Caesar's siege lines were broken, might have ended a lesser commander; Caesar himself reportedly said Pompey did not know how to win a war (Plutarch, Caesar 39). Instead the armies met on 9 August 48 BC at Pharsalus in Thessaly. Though heavily outnumbered, with perhaps 22,000 men against Pompey's 45,000, Caesar anticipated Pompey's plan to outflank him with cavalry under Labienus and concealed a fourth line of veteran infantry to meet it. That line broke the Pompeian cavalry and then collapsed Pompey's exposed wing; his army disintegrated in a single day.

Pompey fled to Egypt, hoping for refuge from the boy-king Ptolemy XIII, whose father he had once helped restore. Instead, on landing near Pelusium on 28 September 48 BC, Ptolemy's advisers, fearing Caesar's anger if they sheltered his rival, had Pompey murdered on the beach. When Caesar arrived in pursuit and was presented with Pompey's head, the ancient sources agree he responded not with triumph but with visible grief at the murder of his former son-in-law and ally (Plutarch, Pompey 80).

The Alexandrian War, Cleopatra and Zela

Caesar's arrival in Alexandria drew him into the Ptolemaic dynastic struggle between Ptolemy XIII and his sister-wife Cleopatra VII. Besieged in the palace quarter through the winter of 48 to 47 BC, Caesar eventually prevailed; Ptolemy XIII drowned in the Nile, and Caesar installed Cleopatra, with whom he had begun a personal and political relationship, as queen alongside a younger brother, Ptolemy XIV. This Egyptian entanglement, unusual for a Roman commander, later became a theme in the hostile tradition about Caesar's ambitions. Moving north to deal with Pharnaces II of Pontus, who had exploited the civil war to seize territory in Asia Minor, Caesar won a rapid victory at Zela on 2 August 47 BC, reporting it to Rome in three words, "veni, vidi, vici" (Suetonius, Divus Iulius 37).

Thapsus, Munda and clementia, 46 to 45 BC

Pompeian resistance did not end at Pharsalus. A substantial optimate force under Metellus Scipio, reinforced by King Juba I of Numidia and by Labienus, regrouped in North Africa. Caesar destroyed it at Thapsus on 6 April 46 BC. In the aftermath, Cato the Younger, commanding the garrison at nearby Utica and unwilling to accept Caesar's clemency or to outlive the free Republic, took his own life, a death the anti-Caesarian tradition swiftly made into a symbol of principled resistance to one-man rule. The very last organised Pompeian army, led by Pompey's sons Gnaeus and Sextus and by Labienus, was destroyed at Munda in Spain on 17 March 45 BC, a battle Caesar reportedly said he fought "for my life" rather than "for victory" (Plutarch, Caesar 56), so hard-fought was it.

Throughout, Caesar made clementia (clemency) a public policy, pardoning defeated Romans rather than proscribing them as Sulla had. He spared Brutus, Cassius and Cicero, and allowed exiles such as Marcellus to return, an act Cicero praised in Pro Marcello (46 BC). Clementia reconciled many former enemies and advertised Caesar as a healer of the Republic. But it carried a sting: a pardon was Caesar's personal gift, so every beneficiary owed his life and standing to Caesar's favour rather than holding it by right, a daily reminder to a senatorial class raised to prize libertas that they now lived at one man's discretion.

The Republic replaced by one man's rule

The military victory was matched by an accumulation of office that emptied the constitution. Caesar's dictatorships escalated from about eleven days in 49 BC, to a second after Pharsalus in 48 BC, to ten successive years in 46 BC after Thapsus, held alongside repeated consulships (48, 46, 45 BC, sole consul in 45) and censorial power. The dictatorship had traditionally been a six-month emergency office; stretched to a decade, and combined with control of elections, armies and the treasury, it left the Senate and assemblies able only to ratify Caesar's wishes. By the end of the war in 45 BC the Republic survived in form, its magistrates, elections and Senate still functioning, but the substance of power had passed permanently to one man. That, more than any earlier crisis, is why the war of 49 to 45 BC is treated as the moment the Republic effectively fell, even though its formal end and the settling of Caesar's succession lay in the further conflicts after 44 BC.

How to read a source on this topic

Sources for the civil war fall into groups with very different reliability profiles, and an exam answer should flag which group a source belongs to. Caesar's own Commentarii de Bello Civili is contemporary and first-hand, but written by the war's chief participant and beneficiary to justify his actions; it is advocacy, not neutral reporting, and conceals as much as it reveals. Cicero's private letters (to Atticus and others) are especially valuable precisely because they were not written for publication, capturing real-time uncertainty rather than a settled verdict. The later narrative historians, Plutarch (Lives of Caesar, Pompey and Cato Minor, early 2nd century AD), Appian (Civil Wars, 2nd century AD) and Cassius Dio (Roman History, 3rd century AD), wrote long after the events, drawing on earlier sources now lost and often shaping material into moral or dramatic narratives; Lucan's epic Pharsalia is later still and openly hostile to Caesar. Archaeological evidence, above all the coinage minted by both sides, is contemporary and physically datable but is propaganda, not neutral record.

Three habits: identify WHO produced the source and WHEN relative to the events; separate what it claims from what it can actually prove; and move deliberately from content, to reliability, to usefulness, to perspective, reaching a judgement rather than merely describing the source.

Model exam responses

1. Source-analysis response (using a reconstructed optimate coin hailing libertas). "A denarius struck by the surviving optimates in Africa in 47 to 46 BC, proclaiming libertas against tyranny, is useful evidence for how the losing side reframed its cause after Pharsalus, shifting from loyalty to the dead Pompey to a broader defence of Republican freedom against Caesar's dominance. Its reliability is limited because it is official propaganda from a defeated command trying to hold its army together, not a neutral record of what soldiers believed. Read alongside the tradition around Cato's suicide at Utica in 46 BC, it corroborates the idea that libertas, symbolised by Cato, became the faction's rallying cry once Pompey was gone."

Marker's note: markers reward using the coin's content to argue about propaganda and morale, rather than only describing what it shows.

2. Essay paragraph (the war as the decisive end of the Republic). "Pharsalus on 9 August 48 BC was the pivot: before it the Senate could still field an army and claim to embody the res publica, but after it the optimate cause survived only as coinage hailing libertas and as Cato's death at Utica. When Caesar took the ten-year dictatorship in 46 BC and struck his own portrait on the coinage, sovereignty had passed to one man in substance if not in name. As Gruen argues, it was the civil war itself, not a slow inevitable decline, that destroyed the Republic; yet, as Syme insists, the war could end this way only because a century of over-mighty commanders had already taught Rome that armies obeyed generals, not the state."

Marker's note: this paragraph scores because it weighs two named historiographical positions to answer the question, rather than asserting a single cause.

Command words and how to use a source

Outline/describe wants a small number of clearly separated, correctly dated points. Explain wants a point, evidence and why it matters. Assess/evaluate/to what extent wants a sustained argument reaching a supported judgement that weighs more than one answer.

Using a source properly means four moves every time: (1) content, what it actually shows or claims; (2) reliability, who produced it, when and for what purpose; (3) usefulness, what specific historical question it can help answer, and how far; (4) perspective, whose viewpoint it represents and what it leaves out. For this dot point, always flag whether a source is a participant's account (Caesar's Commentarii), a contemporary private correspondent (Cicero), a later narrative historian (Plutarch, Appian, Dio) or physical propaganda (coinage), because that single fact usually decides how much weight it can bear.

Weaving in historiography means using a historian's named position to build your argument, for example "as Gruen argues, it was the war itself rather than long decline that ended the Republic," used to support a specific claim, not dropped in as an unconnected quotation.

Common exam traps

Retelling the campaign narrative instead of arguing: Knowing that Ilerda came before Pharsalus, which came before Zela, Thapsus and Munda, is necessary but not sufficient; every essay wants that chronology used to argue about causation and significance, not just recited.
Treating Caesar's Commentarii as a neutral eyewitness account: It is a first-person, self-justifying source written by the war's chief beneficiary; always weigh it against Cicero's contemporary letters or the later narrative historians.
Stopping at Pharsalus or Pompey's death: Organised resistance ended only at Thapsus (46 BC) and Munda (45 BC); a strong answer carries the war through to Munda and Cato's suicide at Utica.

Saying Caesar "made himself king" or "abolished the Republic." He never took the title rex and kept Republican forms; the sharper point is that his accumulating dictatorships and clementia made the Republic one man's rule in substance while leaving its shell.

Historians and the evidence base

Ronald Syme ("The Roman Revolution", 1939) reads the late Republic as an oligarchy being replaced by monarchy through factional violence, with Caesar's victory a decisive stage on the road to Augustus rather than the act of a single ambitious man.

Erich Gruen ("The Last Generation of the Roman Republic", 1974) argues, against narratives of inevitable decline, that Republican institutions remained resilient and that it was the civil war itself, not long-term decay, that destroyed the Republic.

Christian Meier ("Caesar", English translation 1995) describes the Republic's collapse as a "crisis without alternative," arguing the political structures left the elite no workable path back from armed conflict once it began.

Adrian Goldsworthy ("Caesar: Life of a Colossus", 2006) stresses Caesar's personal calculation of risk and the contingency of the outcome, cautioning against reading the war's result as predetermined.

Practice questions

Original practice questions graded from foundation to exam level, each with a full worked solution. Try them before revealing the solution.

foundation3 marksOutline how Caesar seized control of Italy in the first months of the civil war in 49 BC.

Show worked solution →

A 3-mark "outline" needs the trigger, the method and the outcome.

The trigger: On 10 January 49 BC Caesar crossed the Rubicon, the river marking the boundary of his province, with a single legion (the Thirteenth), an act of war under Roman law that began the civil war (1 mark).
The method: He advanced south down Italy with unexpected speed; town after town opened its gates, so that Pompey, short of trained troops and judging Italy indefensible, evacuated the peninsula from Brundisium and crossed the Adriatic to Greece with much of the Senate (1 mark).
The outcome: Within roughly sixty days Caesar controlled the whole of Italy without a major pitched battle, seizing the political centre before his enemies could organise (1 mark).

Marker's note: markers reward the sense of speed and the strategic point (Pompey conceding Italy), not just the fact that Caesar "invaded."

foundation4 marksOutline the defeat of the Pompeians and optimates in the campaigns that followed Pharsalus, from 48 to 45 BC.

Show worked solution →

A 4-mark "outline" needs four correctly dated, clearly separated stages.

Pompey's death (48 BC): After Pharsalus, Pompey fled to Egypt and was murdered on landing near Pelusium on 28 September 48 BC on the orders of Ptolemy XIII's advisers (1 mark).
Zela (47 BC): Caesar crushed Pharnaces II of Pontus at Zela on 2 August 47 BC, reporting the victory as "veni, vidi, vici" (1 mark).
Thapsus (46 BC): He destroyed the Pompeian army of Metellus Scipio and King Juba I of Numidia at Thapsus on 6 April 46 BC, after which Cato the Younger took his own life at Utica rather than accept Caesar's clemency (1 mark).
Munda (45 BC): The last organised resistance, led by Pompey's sons Gnaeus and Sextus and Titus Labienus, was destroyed at Munda in Spain on 17 March 45 BC (1 mark).

Marker's note: markers reward four separate, correctly dated victories rather than a vague statement that Caesar "won the war."

core5 marksExplain the significance of the Battle of Pharsalus (48 BC) for the fall of the Roman Republic.

Show worked solution →

A 5-mark "explain" needs what happened, why it mattered militarily, and its wider significance for the Republic.

What happened: On 9 August 48 BC in Thessaly, Caesar's smaller but veteran army (around 22,000) defeated Pompey's much larger force (around 45,000, heavy in newly raised eastern levies). Caesar hid a fourth line of infantry that broke Pompey's outflanking cavalry under Labienus, then rolled up the exposed wing (1-2 marks).
Why it mattered militarily: Pompey's main field army and the coalition of the Senate's cause collapsed in a single day; Pompey fled and was soon murdered, removing the one commander whose prestige could rival Caesar's (1-2 marks).
Significance for the Republic: Pharsalus broke the optimates as an organised force able to defend the constitution by arms. Though resistance continued to Munda, from this point no institution or coalition could check Caesar, so the effective decision about who ruled Rome had passed from the Senate and people to the victor of a battle (1 mark).

Marker's note: markers reward linking the tactical victory to the constitutional consequence, not just describing the battle.

core6 marksSource A: a reconstructed extract of this type, in the style of Caesar's own Commentarii de Bello Civili, has Caesar declare that after Pharsalus he chose "to conquer by a new kind of victory, and to be safe through mercy and generosity rather than through fear." Using Source A and your own knowledge, explain what the source reveals about Caesar's policy of clementia, and assess its reliability.

Show worked solution →

A 6-mark "explain and assess reliability" needs content, the policy explained, and a reliability judgement with a limitation.

Content: Source A has Caesar presenting mercy (clementia), rather than terror, as a deliberate method of securing victory and reconciling defeated Romans to his rule (2 marks).
The policy explained: This matches Caesar's real conduct: in pointed contrast to Sulla's proscriptions a generation earlier, he pardoned prominent enemies, including Brutus and Cassius, and allowed exiles such as Marcellus to return, praised by Cicero in Pro Marcello (46 BC). Clementia both reduced further resistance and advertised Caesar as a healer of the Republic (2 marks).
Reliability and limitation: Because Caesar wrote and published the Commentarii as the war's chief participant and beneficiary, the framing is self-justifying propaganda; it presents as generosity a policy that also underlined that senators now held their lives and careers by Caesar's personal favour rather than by right, a resentment the source conceals (1 mark).
Judgement: The source is valuable evidence for how Caesar wished his clemency to be understood, but must be checked against Cicero's less partisan contemporary letters before being trusted as a neutral account of its effect (1 mark).

Marker's note: markers reward identifying clementia as both genuine policy and self-interested image-making, not repeating Caesar's framing as fact.

core6 marksExplain how Caesar's accumulating dictatorships between 49 and 45 BC replaced the Republic in practice with the rule of one man.

Show worked solution →

A 6-mark "explain" needs the sequence of powers, how each broke Republican convention, and the overall effect.

The sequence: Caesar held a brief dictatorship of about eleven days in 49 BC to run the elections; a second dictatorship in 48 BC after Pharsalus, with Antony as master of horse; the dictatorship for ten successive years in 46 BC after Thapsus; alongside repeated consulships (48, 46, 45 BC, sole consul in 45) and censorial power as prefect of morals (2 marks).
Breaking convention: The dictatorship had traditionally been a six-month emergency office; stretching it to ten years, and holding the consulship year after year, hollowed out the annual, collegial magistracies that were the heart of Republican government (2 marks).
The effect: By 45 BC no magistrate could be elected, no army raised and no major decision taken against Caesar's will. The forms of the Republic survived, but the substance of power had passed permanently to one man, which is why the escalation ended in dictator perpetuo (February 44 BC) (2 marks).

Marker's note: markers reward explaining how the offices were used to empty the constitution, not just listing the dictatorships.

exam8 marksSource B: a reconstructed coin legend of this type, on a silver denarius struck by a Pompeian commander in North Africa in 47 to 46 BC, hails the cause of Roman liberty (libertas) against tyranny, one of a series of such issues by the remaining optimates after Pharsalus. Using Source B and your own knowledge, assess the usefulness and reliability of coinage as evidence for the cause the losing side claimed to be defending in the civil war.

Show worked solution →

An 8-mark "assess usefulness and reliability" needs content, usefulness, reliability with a limitation, and a judgement.

Content: Source B shows the surviving optimate command in Africa minting coinage that publicly frames their war against Caesar as a defence of libertas against tyranny, rather than as loyalty to the now-dead Pompey (2 marks).
Usefulness: Coinage is contemporary, physically datable and reached soldiers and civilians widely, so it is valuable evidence for how the losing side rebranded its cause after Pharsalus, presenting resistance as the defence of Republican freedom against one-man rule (2 marks).
Reliability and limitation: As official propaganda struck by a defeated faction to sustain morale and legitimacy, the coinage is inevitably one-sided; it shows what the optimate command wanted its troops to believe, not whether ordinary soldiers or provincials actually accepted the "liberty" framing (2 marks).
Judgement: The coinage is therefore most reliable as evidence of optimate self-presentation and morale after 48 BC, and only indirectly useful as evidence of genuine sentiment. It corroborates the literary tradition, reflected in Plutarch's Cato the Younger, that libertas, symbolised above all by Cato's suicide at Utica, outlasted Pompey as the faction's rallying cry (2 marks).

Marker's note: markers reward separating what the coin claims from what it can prove, and using it to argue about wartime propaganda rather than describing its imagery.

exam25 marksTo what extent did the civil war of 49 to 45 BC, rather than any earlier event, mark the effective end of the Roman Republic? In your response, refer to relevant sources and historians' interpretations.

Show worked solution →

A Band-6 response needs a clear thesis, argument lines tied to dated evidence, engagement with historiography, a model paragraph, and a judgement answering "to what extent."

Thesis: The civil war of 49 to 45 BC was the decisive event that ended the Republic in practice, because it transferred final power from the Senate and people to a single victorious general; but it did so by exploiting weaknesses long visible since Sulla, so the war was the moment of death rather than the sole cause.
Argument line 1 - the war destroyed the institutions' capacity to govern: Caesar's seizure of Italy in early 49 BC drove the legitimate government abroad; Pharsalus (9 August 48 BC) shattered the optimate army; and by 46 BC the Senate could only ratify Caesar's ten-year dictatorship. The magistracies still met, but no election, army or decree could go against Caesar's will, so real sovereignty had already left the constitution.
Argument line 2 - the war made one-man rule permanent, not temporary: Unlike Sulla, who resigned his dictatorship and restored senatorial government, Caesar's dictatorships escalated (11 days in 49, a year in 48, ten years in 46, and finally perpetuo in 44 BC). Clementia bound pardoned enemies to his grace rather than restoring them as equals, so even mercy advertised that libertas now depended on one man.
Argument line 3 - but the war exploited a long decay: The precedents were older: Sulla's march on Rome and proscriptions (88 to 81 BC), the private armies of the late Republic, and provincial commands that gave generals personal legions. Pharsalus was possible only because the Republic had already allowed individuals to command armies loyal to themselves rather than the state.
Argument line 4 - the Republic was not yet formally abolished: Caesar kept Republican forms, refused the title rex at the Lupercalia, and the tyrannicides of 44 BC still believed killing him could restore the old order. The war ended the Republic in substance while leaving its shell, which is why the question is one of degree.
Historiography: Ronald Syme ("The Roman Revolution", 1939) reads the whole period as the replacement of an oligarchy by monarchy, with Caesar's victory a decisive stage. Erich Gruen ("The Last Generation of the Roman Republic") argues the Republic's institutions were resilient and that it was the civil war itself, not a long inevitable decline, that destroyed them. Christian Meier's "crisis without alternative" stresses that the elite had no workable path back from armed conflict. Adrian Goldsworthy emphasises Caesar's personal calculation and the contingency of the outcome.
Model paragraph: Pharsalus is the pivot. Before 48 BC the Senate could still field an army and claim to embody the res publica; after it, the optimate cause survived only as coinage hailing libertas and as Cato's suicide at Utica, gestures of a lost side rather than a functioning government. When Caesar was granted the ten-year dictatorship in 46 BC and struck his own portrait on the coinage, the transfer of sovereignty was complete in substance if not in name. As Gruen argues, this was the work of the war itself rather than of slow decay; yet, as Syme insists, the war could only end this way because a century of over-mighty commanders had already taught Rome that armies obeyed generals, not the state.
Judgement: To a large extent the civil war of 49 to 45 BC ended the Republic: it was the event that made one man's rule permanent and irreversible. But it delivered the fatal blow to a body already gravely weakened since Sulla, so it is best judged the decisive cause among several, not the only one.

Marker's note: markers reward a sustained argument answering "to what extent," precise dated evidence (Rubicon 49 BC, Pharsalus 48 BC, ten-year dictatorship 46 BC), named historians (Syme, Gruen, Meier) used to build the case, and a judgement weighing the war against the longer decline rather than asserting one.