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Why did Xerxes invade Greece in 480 BC, how was the campaign fought and lost, and how far can we reconstruct it from the largely Greek and victor-authored sources?

Xerxes and the invasion of Greece 480 to 479 BC: his motives for the campaign; the preparations, including the Hellespont bridges, the Athos canal and the muster at Doriscus; the course of the campaign - Thermopylae and Artemisium, the sack of Athens, the decisive naval defeat at Salamis, the withdrawal to Asia leaving Mardonius, and the final defeats at Plataea and Mycale in 479 BC; an assessment of Xerxes as a commander; and the problems of the largely Greek and victor-authored sources, especially Herodotus and Aeschylus

A focused answer to the HSC Ancient History dot point on Xerxes' invasion of Greece, 480 to 479 BC. His motives, the Hellespont bridges, Athos canal and Doriscus muster, Thermopylae and Artemisium, the sack of Athens, the decisive defeat at Salamis, the withdrawal leaving Mardonius, Plataea and Mycale, Xerxes as commander, and the problem of the Greek victor sources.

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

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Quick answer

Xerxes (king from 486 BC) invaded Greece in 480 to 479 BC to avenge Marathon (490 BC) and the Ionian Revolt, to expand the empire and to prove himself as Great King, urged on by Mardonius over Artabanus' caution (Herodotus 7.8 to 11). He prepared with famous engineering, the Hellespont boat-bridges, the Athos canal and pre-stocked depots, mustering at Doriscus, where Herodotus gives his vastly inflated figures (about 1.7 million infantry, 1,207 ships), which modern historians reject as impossible. In 480 BC the Persians forced Thermopylae (with the simultaneous, indecisive sea battle at Artemisium) and burned an evacuated Athens, but were decisively beaten at sea at Salamis, engineered by Themistocles in the narrows. Xerxes withdrew to Asia, leaving Mardonius, whose defeats at Plataea and Mycale in 479 BC ended the invasion. As a commander Xerxes was a strong organiser but made the fatal choice at Salamis. Every reconstruction depends on Greek, victor-authored sources, above all Herodotus and the near-contemporary tragedy of Aeschylus (Persae, 472 BC), so numbers and the hubris-driven portrait of the king must be read critically.

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What this dot point is asking
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How to read a source on this topic

What this dot point is asking

This dot point covers the second Persian invasion of Greece, the great campaign Xerxes led in person in 480 to 479 BC. You need to be able to explain WHY he invaded (the motives), HOW he prepared (the famous engineering feats and the muster), what actually HAPPENED across the two campaigning seasons (Thermopylae and Artemisium, the sack of Athens, the decisive defeat at Salamis, the withdrawal, and the final Greek victories at Plataea and Mycale), and how to ASSESS Xerxes as a commander. Running through all of it is a source problem: almost everything we know comes from Greek, victor-authored writing, above all Herodotus and Aeschylus, so the numbers and the portrait of Xerxes have to be handled critically rather than taken at face value.

In plain English

Think of Xerxes as a new CEO who inherits a huge, successful company and one piece of unfinished business: a smaller rival that humiliated the firm before he took over (Athens at Marathon). He decides to crush it, and he plans the takeover on a massive scale, building the logistics first (bridges, a canal, stockpiled supplies) before moving. At first it works: he smashes through the rival's front-line defence (Thermopylae) and occupies its headquarters (Athens). Then he makes one big, avoidable mistake, fighting the decisive battle on ground that throws away his size advantage (the narrows at Salamis), loses, panics, and heads home, leaving a deputy to finish the job. The deputy loses too. The twist for a historian is that the only detailed write-ups of the takeover were produced by the RIVAL's side, years later, keen to make their survival look heroic and the CEO look arrogant, so you have to read every "fact", especially the giant numbers, with that in mind.

The answer

Xerxes' motives for the invasion

Xerxes came to the throne in 486 BC and inherited a war his father Darius I had left unfinished. Darius had been humiliated at Marathon in 490 BC and was preparing a second expedition against Greece when he died. Several motives combined:

Revenge. Athens and Eretria had supported the Ionian Revolt (499 to 494 BC) against Persian rule and had shared in the burning of Sardis; Marathon then added a direct military insult. Punishing Athens was a matter of royal honour.
Imperial expansion and the duty of a Great King. A new king was expected to extend the empire and demonstrate divine favour. Conquering Greece would carry Persian power into Europe.
Court pressure. Herodotus (7.8 to 11) dramatises a council in which Mardonius, ambitious for a European command, presses the young king to invade, while Xerxes' uncle Artabanus warns against the risks of bridging the Hellespont and trusting so much to the fleet. The debate, and the dreams that follow it, are Herodotus' literary way of exploring motive; they should not be read as a verbatim record.

The preparations: the Hellespont bridges, the Athos canal and Doriscus

Xerxes' preparations were on a scale designed to overawe. Two feats dominate the tradition and the exam:

The Hellespont bridges. Persian engineers built two bridges of boats lashed together across the Hellespont near Abydos so the land army could march from Asia into Europe. Herodotus (7.34 to 36) records that a first attempt was destroyed by a storm and that Xerxes, in fury, had the strait "punished", an anecdote that tells us more about how the Greeks wished to portray the king's pride than about Persian engineering.
The Athos canal. A canal was cut through the neck of the Athos peninsula so the fleet could avoid rounding Cape Athos, where a Persian fleet had been wrecked in a storm in 492 BC during Mardonius' earlier campaign. Traces of the cutting have been identified by modern survey, so this is one preparation with independent archaeological support.
Supply and muster. Depots of food were stockpiled in advance along the Thracian route, and the combined army and fleet were assembled and reviewed on the plain of Doriscus in Thrace. It is at this muster that Herodotus gives his enormous numbers, discussed below.

The problem of the numbers

Herodotus reports the land army mustered at Doriscus as about 1,700,000 infantry, with the fleet at 1,207 triremes, and totals for the whole expedition, once camp followers are added, running into the millions. These figures are almost universally rejected by modern historians as impossible. An army of that size could not have been supplied with food and water on the available roads, and the numbers function in the Greek tradition to magnify the achievement of the small Greek coalition that defeated it. Modern estimates of the actual combatant strength vary widely and are far smaller (commonly placed in the low hundreds of thousands or less for the land forces, and several hundred to perhaps around a thousand ships), but these are reconstructions from logistics, not counts, and should be treated as illustrative rather than firm. What is secure is that the force was genuinely very large and drawn from across the empire; the precise size is not recoverable.

The campaign of 480 BC: Thermopylae, Artemisium and the sack of Athens

In the summer of 480 BC the Persian host advanced through Thrace, Macedonia and Thessaly. The Greek coalition (led by Sparta, with Athens supplying the fleet) chose to hold two linked chokepoints together: the narrow pass of Thermopylae on land and the strait off Artemisium at sea.

Thermopylae. A small Greek force under the Spartan king Leonidas, perhaps around seven thousand men, held the pass for several days against overwhelming numbers. They were undone when a local Greek, Ephialtes, revealed the Anopaea mountain path, allowing the Persians to outflank the defenders. Leonidas and his 300 Spartiates, with Thespians and others, fought to the death, a rearguard action that became the enduring symbol of Greek resistance.
Artemisium. Fought at the same time, the naval engagements off Artemisium were costly and indecisive; on news of Thermopylae the Greek fleet withdrew south.
The sack of Athens. With central Greece open, the Persians moved into Attica. On Themistocles' urging the Athenians had evacuated the city (justified by reinterpreting the Delphic "wooden walls" oracle as the fleet), so the Persians occupied a largely empty Athens in September 480 BC and burned the Acropolis. This was a real strategic success for Xerxes, and it is important not to skip it: the invasion was winning at this point.

Salamis: the decisive defeat

The turning point came in the narrow straits off the island of Salamis in late September 480 BC. Themistocles engineered the battle, reportedly sending a secret message (via his servant Sicinnus) that lured the Persian fleet into the confined water between Salamis and the Attic coast, where its numbers became a liability rather than an advantage. The Greek fleet inflicted a heavy defeat. Herodotus (8.90) pictures Xerxes watching the disaster from a throne on the slopes of Mount Aigaleos, a scene that is as much a moral tableau of pride humbled as a piece of reportage.

Salamis was decisive because it broke Persian control of the sea. Without naval superiority Xerxes could not guarantee the supply lines and the Hellespont crossing on which his whole army depended. Fearing (again on Themistocles' prompting) that the Greeks might sail to destroy the bridges and trap him in Europe, Xerxes withdrew to Asia with a large part of the army, leaving his general Mardonius with a picked force to winter in Greece and finish the campaign.

The end: Plataea and Mycale, 479 BC

In 479 BC Mardonius reoccupied Athens, then withdrew into Boeotia, where the largest Greek land army yet assembled, commanded by the Spartan regent Pausanias, defeated and killed him at Plataea. In the same season the Greeks won at Mycale, on the Ionian coast across the Aegean, destroying the remnant of the Persian fleet and encouraging the Ionian cities to revolt. With these two victories the invasion was over. Xerxes himself never returned to the Greek front.

Xerxes as a commander: an assessment

A balanced verdict avoids both the Greek caricature of a vain despot and an uncritical rehabilitation.

In his favour: the preparation was genuinely impressive. The bridging of the Hellespont, the Athos canal, the advance supply depots and the coordinated army-and-fleet advance show real strategic organisation, and the campaign came close to succeeding: Thermopylae was forced and Athens taken within a single season.

Against him: the decisive failures were his. Accepting battle at Salamis, in narrow water that cancelled his numerical advantage and against cautious advice (Herodotus 8.68 to 69 gives the warning to Artemisia of Halicarnassus), was the pivotal error. The subsequent withdrawal, though defensible as protecting his communications and person, removed the king and much of the army from the theatre and left the unfinished war to Mardonius, who lost it. Herodotus frames the retreat as fear; the strategic logic is arguable, but the outcome was fatal to the enterprise.

The fairest assessment is that Xerxes was a capable organiser and a poor battle commander at the one moment that mattered, and that Persian defeat also owed much to Greek leadership (Themistocles above all) and to the logistics of holding so large a force together far from home.

How to read a source on this topic

Almost all the narrative evidence for this dot point is Greek and victor-authored, so source-handling is central. Three habits.

First, identify the KIND of source and its distance from the events. Herodotus (Histories, writing some decades after) is our main continuous narrative, rich but late and shaped by oral tradition and moral patterning. Aeschylus (Persae, 472 BC) is near-contemporary and, by tradition, a veteran of the wars, but it is a tragedy staged for an Athenian audience, not a report. Persian royal inscriptions (such as Xerxes' building and religious texts) survive but give ideology, not a campaign narrative, so there is no continuous Persian account to set against the Greek one.

Second, watch for the two recurring distortions: inflated numbers (treat Herodotus' millions as illustrative of scale and of Greek perception, not as counts) and the hubris frame (Xerxes whipping the Hellespont, enthroned to watch Salamis), which tells you how the Greeks wished to remember the king as much as what he did.

Third, always move from content to reliability to usefulness to perspective and reach a judgement, rather than retelling the story the source tells.

Model exam responses

1. Source-analysis response (using an extract in the style of Aeschylus' Persae). "A passage in the manner of Aeschylus' Persae, narrating Salamis from the Persian court as a divinely caused catastrophe, is useful as near-contemporary evidence, since Aeschylus was writing in 472 BC for an audience that had lived through the war and may himself have fought in it. Its reliability is limited by genre and purpose: it is a tragedy built on hubris and divine retribution, staged to celebrate Athenian deliverance, so its Persian 'voice' is a Greek construction. It is therefore strong evidence for how Athens interpreted its victory, and only indirect evidence for Persian decision-making."

Marker's note: markers reward candidates who separate a source's contemporaneity (a strength) from its genre and audience (a limitation), rather than treating "early" as automatically "reliable".

2. Essay paragraph (Xerxes' responsibility for Salamis). "The strongest case against Xerxes rests on Salamis. Having already taken Athens, he needed only to preserve his fleet and exploit Greek disunity, yet he accepted battle in the one setting that erased his advantage in numbers. Herodotus (8.68 to 69) has Artemisia warn against exactly this, and stages the king enthroned to watch the disaster, a scene shaped by the Greek theme of pride punished. Read past that moralising, the substance survives: the decision to fight in the narrows was the king's, it was warned against, and it was the hinge of the campaign. That makes Xerxes materially responsible for the defeat, even after we discount the hostile framing around him."

Marker's note: this paragraph scores because it uses the source's bias as part of the argument (distinguishing the moral frame from the underlying decision) rather than either accepting or dismissing Herodotus wholesale.

Command words and how to use a source

Outline/describe wants a few clearly separated points; explain wants a point, evidence and why it matters; assess/evaluate/to what extent wants a sustained argument reaching a supported judgement about the question asked (for this topic, usually Xerxes' motives, the causes of failure, or the value of the sources).

Using a source properly means four moves every time: (1) content, what does it show or say; (2) reliability, who produced it, when, and for what purpose; (3) usefulness, what specific question can it help answer, and how far; (4) perspective, whose viewpoint is it, and what does that leave out. For this dot point, always fix whether a source is contemporary (Aeschylus, 472 BC) or later (Herodotus), and whether it is Greek/victor (nearly all of it) or Persian (mostly ideological inscriptions).

Weaving in historiography means using a named position to build your case, for example "as Briant cautions, the Greek tradition casts Xerxes as a hubristic tyrant, so his 'responsibility' is partly a Greek literary construct", used to qualify a claim, not dropped in as decoration.

Common exam traps

Retelling the battles instead of arguing: A question on motives, on the causes of failure, or on the sources wants an argument, not a blow-by-blow of Thermopylae and Salamis. Use the events as evidence for a case.
Taking Herodotus' numbers literally: Writing that Xerxes led "1.7 million men" or "over five million" as fact will cost you. Flag them as inflated and treat them as illustrative of scale and Greek perception.
Collapsing the two seasons: Thermopylae, Artemisium, the sack of Athens and Salamis are all 480 BC; Plataea and Mycale are 479 BC. Do not put Plataea in the wrong year or before Salamis.
Forgetting the source problem: Almost everything is Greek and victor-authored. An answer that never mentions that Herodotus and Aeschylus are Greek accounts, with the biases that implies, is incomplete at this level.

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 Xerxes' motives for invading Greece in 480 BC.

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A 3-mark "outline" needs three distinct, clearly separated motives.

Revenge and unfinished business: Xerxes inherited from his father Darius I the goal of punishing Athens and Eretria for aiding the Ionian Revolt (499 to 494 BC) and for the Persian defeat at Marathon in 490 BC (1 mark).
Imperial expansion and royal duty: As the new Great King (from 486 BC), Xerxes was expected to enlarge the empire and prove his fitness to rule; Herodotus presents the conquest of Greece as extending Persian dominion to the edge of Europe (1 mark).
Pressure at court: Herodotus (7.8 to 11) shows Mardonius urging invasion for glory and personal ambition, so that the decision was also shaped by advisers pushing the young king toward war (1 mark).

Marker's note: markers reward three separate motives (revenge, expansion, court pressure) rather than one motive explained at length.

foundation4 marksDescribe the major engineering and logistical preparations Xerxes made for the invasion of Greece.

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A 4-mark "describe" needs several concrete preparations with a supporting detail each.

The Hellespont bridges: Xerxes' engineers built two bridges of boats lashed together across the Hellespont near Abydos, allowing the land army to march from Asia into Europe; Herodotus says an earlier attempt was destroyed by a storm and rebuilt (1 mark).
The Athos canal: A canal was cut through the neck of the Athos peninsula in the northern Aegean so the fleet could avoid rounding Cape Athos, where a Persian fleet had been wrecked in a storm in 492 BC (1 mark).
Supply arrangements: Provision depots were stockpiled in advance along the Thracian coast and rivers, and subject peoples were levied for troops, ships and food to sustain the march (1 mark).
The muster at Doriscus: Xerxes assembled and reviewed the combined land army and fleet on the plain of Doriscus in Thrace, the point at which Herodotus gives his (much-inflated) numbers (1 mark).

Marker's note: markers reward accurate, specific preparations (bridges, canal, depots, muster) rather than a general statement that Xerxes gathered a large army.

core5 marksSource A: an ExamExplained reconstruction, in the manner of Herodotus' council scene, has the general Mardonius urge the king to avenge Marathon and win glory in Europe, while the elder adviser Artabanus warns that so vast an expedition risks over-reach by land and sea. Using Source A and your own knowledge, explain what the council debate reveals about the decision to invade Greece.

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A 5-mark "explain" using a source needs use of the source, the point it reveals, and supporting knowledge.

Use of the source: Source A stages the decision as a genuine debate between an ambitious general pressing for war (Mardonius) and a cautious elder warning of over-reach (Artabanus), rather than a single royal command (2 marks).
What it reveals: It shows the invasion as a contested choice in which the young king was pulled between the prestige of conquest and warnings about the scale and risk of the enterprise, so that the decision reflects court politics and Xerxes' need to prove himself, not just strategic necessity (2 marks).
Supporting knowledge: In Herodotus (7.8 to 11) Mardonius argues for revenge and expansion while Artabanus, Xerxes' uncle, warns against bridging the Hellespont and trusting the fleet; the debate, and the dream sequence that follows, is a literary device Herodotus uses to explore motive and to foreshadow disaster (1 mark).

Marker's note: markers reward candidates who read the debate as Herodotus' framing of motive and risk, and who note it is a constructed set-piece, not a verbatim transcript.

core6 marksExplain why the Battle of Salamis (480 BC) was the decisive engagement of the Persian invasion.

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A 6-mark "explain" needs the outcome, why it mattered strategically, and its consequences.

The outcome: In the narrow straits off Salamis in late September 480 BC, the Greek fleet under the Athenian Themistocles and the Spartan Eurybiades destroyed a large part of the Persian navy, which had been lured into water too cramped for its numbers (2 marks).
Why it mattered strategically: The narrows cancelled the Persian numerical advantage, and the defeat threatened Xerxes' sea communications and the Hellespont bridges on which his army depended; without naval control he could not safely supply or reinforce a prolonged campaign in Greece (2 marks).
Consequences: After Salamis Xerxes withdrew to Asia with much of the army, leaving Mardonius with a picked force; the following year (479 BC) that force was defeated on land at Plataea and the Persian remnant at Mycale, ending the invasion (2 marks).

Marker's note: markers reward the causal link from the narrows to the loss of naval control to Xerxes' withdrawal, not just a narrative of the fighting.

core6 marksSource B: an ExamExplained reconstruction, in the manner of the review at Doriscus, records a Persian land army of more than 1.7 million fighting men drawn from dozens of subject nations, mustered and counted on the plain. Using Source B and your own knowledge, assess the reliability and usefulness of such figures as evidence for the size of Xerxes' army.

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A 6-mark "assess" needs content, reliability, usefulness and a judgement.

Content: Source B, echoing Herodotus' account of the muster at Doriscus, presents a colossal multi-national land army of over 1.7 million men, counted at a single review (1 mark).
Reliability: Such figures are highly unreliable as literal counts. They come from a Greek account written decades after the events, and modern historians from Hans Delbruck onward have shown that an army of this size could not have been fed, watered or marched along the available roads; the numbers serve to magnify the Greek achievement (2 marks).
Usefulness: They remain useful, but as evidence of a different kind: they show how the Greeks remembered and dramatised the invasion as a David-and-Goliath struggle, and they confirm that the force was genuinely very large and drawn from across the empire (2 marks).
Judgement: The figure is best treated as illustrative rather than statistical: modern estimates of the actual combatant strength vary widely and are far lower (often placed in the low hundreds of thousands or less), so the source is reliable for Greek perception and Persian diversity, not for a precise headcount (1 mark).

Marker's note: markers reward candidates who reject the literal figure, explain WHY (logistics, victor perspective, late Greek authorship) and still salvage a use for the source.

exam8 marksSource C: an ExamExplained reconstruction, in the style of Aeschylus' tragedy Persae, has a Persian messenger lament before the royal court that a god deceived the king into fighting in the narrows at Salamis, where the crowded fleet was destroyed and Persia's finest men drowned. Using Source C and your own knowledge, assess the usefulness and reliability of the Greek victor sources for reconstructing the Persian invasion.

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

Content from the source: Source C, in the manner of Aeschylus' Persae (performed at Athens in 472 BC), shows the defeat at Salamis narrated from the Persian side as a catastrophe caused by a god deceiving the king into fighting in the narrows (2 marks).
Usefulness: The Greek sources are indispensable: without Herodotus' Histories and Aeschylus' Persae we would have almost no narrative of the campaign at all, since no continuous Persian account survives. Aeschylus is especially valuable as a near-contemporary who, by tradition, fought in the wars, and Herodotus preserves detail on preparations, battles and personalities (3 marks).
Reliability and limitation: Both are Greek, victor-authored and shaped for Greek audiences. Aeschylus is a tragedy built around hubris and divine punishment, staged to celebrate Athens, not a report; Herodotus, writing some decades later, inflates numbers and frames Xerxes as an arrogant tyrant whose fall is deserved. Both risk projecting Greek moral patterns onto Persian decisions (2 marks).
Judgement: The Greek sources are highly useful because they are almost all we have, but their reliability must be handled critically: they are strong on the Greek experience and the broad course of events, weaker and biased on Persian motive and numbers, so they are read against Achaemenid evidence and modern logistical analysis (1 mark).

Marker's note: markers reward candidates who hold usefulness and reliability apart, recognise the near-monopoly of Greek sources, and use the hubris framing as evidence of bias rather than fact.

exam25 marksTo what extent was Xerxes himself responsible for the failure of the Persian invasion of Greece? In your response, refer to relevant sources and historians' interpretations.

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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. Xerxes bears real and significant responsibility, above all for accepting battle at Salamis and for the withdrawal that followed, but the failure was over-determined: Greek strategy, the structural difficulty of commanding so vast a force, and the moralising shape of the Greek sources all share in the outcome. Xerxes is a major, not the sole, cause.

Argument line 1: the invasion was formidably planned, so failure is not simple incompetence. The Hellespont bridges, the Athos canal, pre-stocked supply depots and the Doriscus muster show serious strategic preparation; the campaign nearly succeeded, forcing Thermopylae and taking Athens by September 480 BC. Any verdict on Xerxes must start from a plan that came close to working.

Argument line 2: Salamis was the king's decisive error: Herodotus (8.68 to 69) has the Carian queen Artemisia advise against fighting in the narrows; Xerxes overruled such caution and let Themistocles' ruse (the message via Sicinnus) draw his crowded fleet into water that cancelled its numbers. The pivotal defeat flowed from a royal decision.
Argument line 3: the withdrawal was defensible but costly: Leaving Mardonius with a picked force while the king returned to Asia protected the Hellespont crossing and the king's person, but it removed Xerxes and much of the army from the theatre; Mardonius' defeats at Plataea and Mycale in 479 BC then ended the war. Herodotus frames the retreat as fear, though the strategic logic is arguable.
Argument line 4: causes beyond Xerxes: Greek unity and leadership (Themistocles at Salamis, Leonidas at Thermopylae, Pausanias at Plataea), terrain that neutralised numbers, and the sheer logistics of feeding a huge multi-national army made Persian defeat likely regardless of the king. The outcome was over-determined.
Historiography: Peter Green and J.F. Lazenby credit Themistocles' generalship as decisive, shifting weight away from Xerxes' errors alone. On the sources, Pierre Briant and Amelie Kuhrt caution that the Greek tradition casts Xerxes as a hubristic tyrant and treats the campaign as an existential clash, whereas from the Achaemenid side it was a costly frontier reverse, not a collapse. On numbers, Delbruck and Green regard Herodotus' figures as impossible.
Model paragraph: The clearest case for Xerxes' responsibility is Salamis. Having taken Athens, he needed only to preserve his fleet and starve a divided Greece, yet he accepted battle in the one setting that erased his advantage. Herodotus stages the king enthroned on the slopes of Mount Aigaleos to watch the disaster, a scene that is also a moral tableau of pride punished. Read critically, past the hubris framing, the substance remains: the decision to fight in the narrows was the king's, it was warned against, and it was the hinge on which the invasion turned. That makes Xerxes materially responsible, even after we discount the Greek moralising around him.
Judgement: To a considerable but not sole extent: Xerxes' choice at Salamis and his subsequent withdrawal were decisive Persian failures, but Greek leadership, logistics and the biased shape of the evidence mean responsibility cannot rest on the king alone.

Marker's note: markers reward a sustained argument answering "to what extent" rather than a battle narrative, precise dated evidence, named historians used to build the case, and explicit awareness that the Greek sources shape "Xerxes' responsibility" as much as they report it.