2500 years ago this year a massive Persian force descended into Greece. How massive we cannot say. Ancient figures for Persian numbers are wildly exaggerated from the very start. Just a few years after the war an inscription at Thermopylae, site of the first engagement between Greek forces and the invaders, gave a figure of 3 million for the land army. Modern figures by different means generally reduce that figure to about 200,000. Even that may be far too high. But on any calculation this was the biggest force ever seen on the Greek peninsula at that date.

At its head was the Persian king Xerxes, new to the throne, who had come to avenge the defeat at Marathon of an army sent by his father Darius against Athens ten years earlier. This time the force was far larger, and unlike the previous invasion, which came by sea, this time it was joint land and sea operation, supported by carefully placed supply dumps in friendly territory, and elaborate engineering works; a canal was dug through Mount Athos to allow the fleet to avoid the treacherous seas around the peninsula, and a double pontoon bridge was built across the Hellespont. The scale of this expedition made clear that the aim was not punish but to conquer and stay. Our earliest source, Herodotus, presents the expedition as more ambitious still, as the first step in an attempt to absorb Europe into the empire. It seems unlikely that this was a strategic goal at this point. But with Greece taken there was nothing to prevent Persia from expanding restlessly westward as it had expanded eastward across Asia.

The Persian army rolled relentlessly south through Greece, accepting surrenders as it progressed seemingly unstoppably, while the Greeks struggled to put together an alliance capable of responding. They did however send a small allied force about 7,000 strong to the narrow pass at Thermopylae in central Greece with 300 Spartans at its core. The terrain was chosen to neutralize the Persian numbers and prevent them from using their cavalry and limiting the impact of their formidable archers. In a determined defence over two days which surprised the Persians the Greek forces threw back repeated attacks until the Persians sent a force through the hills to take the Greeks in a pincer movement. A substantial number of the Greeks were able to slip away, while the commander, the Spartan king Leonidas, stayed behind with a rear guard which included the 300 Spartans. On the third, bitter day of fighting, the rear guard held out doggedly until the Persians eventually lost patience and shot them down with arrows, before rolling south to sweep into Attica and burn Athens. And so Thermopylae became the archetypal rear guard action of Europe and its diaspora.

While the land armies were clashing at Thermopylae, the fleets were fighting at Artemisium in the strait between Euboea and Mount Pelion in far less decisive actions. But it was the fleet which broke the momentum of the Persian advance in September 480, probably about a month after the battle of Thermopylae. The Greek fleet fell back on Salamis, where the Athenians had evacuated their non-combatants. Many of the southern Greeks wished to fall back beyond the Isthmus of Corinth, an intelligible strategy but one which would have made it difficult if not impossible to regain the northern half of Greece, and which would still leave the southern Greeks exposed to attack, while the Persian fleet remained intact. It was the Athenian Themistocles who forced the issue by tricking the Persians into a hasty attack in the strait between Salamis and the mainland of Attica.

Salamis allowed the Greeks to repeat the strategy of Thermopylae by drawing the Persians into a narrow space where the smaller Greek fleet could manoeuvre and the Persians would not only be unable to use their superior naval skills but would struggle to avoid colliding with each other. The strategy was risky, since a Greek defeat might destroy the Greek fleet and leave Persia dominant by land and sea. But the risk paid off. Xerxes convinced that he was dealing with a demoralized and divided enemy, advanced his fleet into the strait, where it was decisively defeated. Modern scholars have argued not unreasonably that there was no overwhelming need to engage the Greek fleet. He could have blockaded it with part of his fleet and moved on by land and sea, while letting inevitable Greek divisions do their work. Instead he fought in space dictated by his enemy and lost.

Salamis represented a serious setback for the Persians. But though the Persian fleet – and the king – withdrew after the defeat, the army remained in Greece over the winter under Xerxes’ general (and kinsman) Mardonius. Without the fleet its prospects of pressing into southern Greece against a determined defence of the Isthmus of Corinth were poor. It was however still in a position to consolidate the Persian domination of the rest of the peninsula. And there was still the prospect of the return of the Persian fleet. But a year later in 479 in a hard fought and shifting battle a massed Greek force faced and defeated the Persian army at the battle of Plataea in Boeotia. The Greek victory was sealed in a further battle at Mycale on the southern coast of Asia Minor, when the Greeks decisively defeated a Persian army and destroyed the fleet. The invasion was done and there was never another.

The Greeks liked to think that the defeat of the expedition was disastrous for Persia. The losses were enormous. But the empire could absorb them and any backlash at home, if there was one, had no destabilizing effect, on the regime, on Xerxes’ career or on the empire. It was in contrast vitally important for Greece, since it cemented in place and enhanced the widespread sense of Greek uniqueness and superiority to ‘barbarian’ non-Greeks already well under way. And the invasion had an enormous impact on Greek relations with Persia and on interstate Greek politics for the best part of two centuries, culminating in Alexander’s invasion (and destruction) of the Persian empire.

It is interesting to speculate what might have happened, if the invasion had succeeded. What we can be sure of is that the subsequent history of Greece would have been very different. So too would that of Europe, if the Persians had continued their incremental expansion of the empire westward. But even if the Persians had settled for controlling Greece, the importance of Rome’s reception of Greek, especially Athenian, culture as it ultimately evolved, and the impact of that on the Renaissance, mean that the western world as we know it would have differed in a wide variety of ways, even if we can only speculate what those might have been. So the invasion was a pivotal moment.

It is this pivotal moment which forms the focus of the essays and chapters contained in this selection of works from the classical journals. It designedly contains work published at different periods over the last century. It makes no attempt at comprehensive cover, if that were possible. But it does contain some superb scholarship, and hopefully food for thought.