The Persians at the start of Cyrus’s career seem to have had no cavalry, but the Medes, whom they incorporated into their kingdom, were famous horse soldiers. The value of their mobility and striking power in the open plains of the Middle East was quickly apparent to the Persians. Their aristocracy were probably already in the habit of riding and hunting and this enabled them to develop quickly into horse-soldiers. As their empire expanded into the southern steppe of Asia and the Indus valley the qualities of cavalry became ever more valuable and the Persian aristocracy soon developed an enormous enthusiasm for fighting on horseback. Herodotus tells us that young Persian nobles were above all instructed in this form of warfare:
Their sons are carefully instructed from their fifth to their twentieth year, in three things alone, – to ride, to draw the bow, and to speak the truth. Until their fifth year they are not allowed to come into the sight of their father, but pass their lives with the women. This is done that, if the child die young, the father may not be afflicted by its loss.
This does not mean that Persians had no infantry; their ‘Immortals’, so-called because every casualty was automatically replaced, were an elite corps of 10,000 in close attendance on the monarch, and plenty of other foot soldiers were raised within their empire, especially archers. But the finest troops, the aristocracy and their followers, were concentrated in the cavalry. And the Persians understood the difference between victory, which was a military achievement, and conquest which demanded the creation of a political basis for the new regime. Because of this, although they imposed Persian governors (satraps) on the people they conquered, they were at pains to respect their customs and religion and to allow important native leaders to retain authority. This enabled the Persians to recruit from these conquered peoples to create ever bigger armies, and gave them access to a very wide range of native skills. For example, to attack Egypt Cambyses needed a fleet, and he was able to recruit this from the subjugated Phoenician cities of the Mediterranean coast in what is now Lebanon. Raising troops was made easier because across the Middle East a common system of granting land to soldiers in return for military service already prevailed, while, universally, great men were expected to bring their armed followings to serve the king. This tolerant policy explains the enormous military capacity of the Persian Empire.
When Xerxes (485–465 BC) invaded Greece in 480, his host was said to number 5,283,220, organised in innumerable ethnic contingents. Historians have unanimously condemned this vast figure, and it is now generally believed that Xerxes had about 210,000 soldiers and that the core of the army consisted of Persian, Iranian and Indo-Iranian troops under Persian command. But even if we assume that many of these were servants and support troops rather than fighters, it was a huge army. The Persians organised their forces systematically on a decimal system, with divisions of 10,000 men subdivided into regiments of 1,000, in turn divided into units of 100 and 10. An elaborate logistical service supported the soldiers, and roads were quickly built to link the empire, notably the ‘Royal Road’ from Sardis in the west to Susa in the Persian heartland, along which dispatch riders maintained communications.
The core of the Persian army was formed by elite units. The Persian aristocracy had enormous wealth, enabling them to afford the finest horses for themselves and their retainers. This meant that the finest soldiers in the Persian Empire were concentrated in the cavalry. The best infantry units, like the famous ‘Immortals’, came from the Iranian heartlands, and were of very high quality. These forces were supported by provincial levies of horsemen and infantry drawn from anywhere between what is now Pakistan and western Anatolia. They were of more variable quality, and very large numbers of the foot were only lightly armed troops, many of them archers. This balance of forces would prove crucial in the confrontation with the Greeks.
The remarkable achievement of the Achaemenids becomes more apparent when viewed from a global perspective. In China, the period of the Later or Eastern Zhou (771–221 BC) was one of intense warfare between a series of states which, to a greater or lesser extent, shared a common Han culture. As the power of the Zhou dynasty shrank to a mere localised authority around Luoyang, some fifteen major states emerged, and a myriad lesser ones. The most important were the Qi of modern Shandong and the Jin of modern Shaanxi, while to the south Chu and Wu were the major powers along the Yangtze. In all the states the kings enlisted the support of the gentry, the shi, who helped to forge governmental bureaucracies, thereby reducing the authority of the great aristocrats. Confucius (551–479 BC) came from the shi, and he created for them an ideology of government emphasising balance and moderation in all things, and in particular the spirit of reciprocity by which one would ‘never impose on others what you would not choose for yourself’. This philosophy very quickly became central to Chinese culture. At the same time the Chinese economy flourished. Trade was fostered, partly because the adoption of money, which seems to have appeared simultaneously in all the world civilisations in the sixth century BC, made it easier. The art of metallurgy became highly advanced. These were impressive developments, but the Chinese states were simply not on the scale of the Persian Empire. Perhaps what distinguished them was the relentless insistence that conquered peoples should conform to ‘Chinese’ cultural norms, in contrast to the Persian practice of tolerance and incorporation of such differences.
Chinese armies about 500 BC, according to Sun Tzu, were enormous infantry forces, as large as 100,000, within which chariots provided officers with mobility and a clearly visible rallying point for their followers. Chinese metal-workers produced splendid bronze weapons. The increasing use of armour and swords are a clear indication that the close-quarter infantry battle was becoming more common. One consequence of this remarkable skill in metallurgy was the invention, probably in the fifth century BC, of the crossbow. The crucial part of this weapon was the bronze trigger-lock which held the bowstring, and some superbly worked examples have survived. This mechanical bow was primarily a weapon of the infantry, and was particularly useful in defending and attacking fortifications. However, it was used in huge numbers and this may, in part, account for another distinctive characteristic of Chinese warfare at this time: the lack of cavalry. Of course, horses were known and ridden, but the sheer firepower of Chinese infantry must have made chariots and mounted men appear redundant. Most decisively, sieges dominated Chinese warfare, encouraging a labour-intensive style of war. Chinese military development was unusual because of the absolute dominance of infantry, in marked contrast to Persian warfare which turned upon cavalry. However, the underlying process of state centralisation, reducing aristocrats to state service, has been noted in the Persian Empire.
Northern India, specifically the Indus and Ganges valleys, also formed a distinct cultural unity which was sharply divided. In the sixth century BC some sixteen states can be traced in this vast area, of which the most important were Magadha and Kosala in the Ganges valley. All, to a degree, shared the Aryan heritage of a caste system which divided society into the priestly learned Brahmans, the warriors or ksatriya, the bulk of the population of presumed Aryan origin, the dvija, and finally the despised native population or dasa. In addition, the Hindu pantheon of gods was clearly ascendant. Increasingly these people inhabited timber cities like Sravasti in Kosala or Rajgir in Magadha enclosed by strong earthwork walls. Despite the political divisions and wars, this was an age of great intellectual and religious vigour, from which Siddhrtha Gautama, the Buddha (between 563 and 483 BC) arose. It was also an age of trading vigour in which Taxila formed a vital connection with Persia through which commodities like horses, gold, textiles and precious stones passed. It was probably because of this exchange that the Aramaic script of the Middle East was adopted in India. The Aryans of India were horse-people, but for their armies they also mobilised huge infantry masses who fought in close order alongside chariots and cavalry. Their armies, therefore, resembled those of the Persians, except that they also used war-elephants which could trample their enemies.
Persia was a global superpower with long frontiers which ebbed and flowed. It suffered from the same weaknesses as all ancient empires. It was difficult to control distant provinces, especially when succession disputes in the ruling house of the Achaemenids were quite frequent, and factional struggles amongst the elite were troublesome. The personality of the ruler was always crucial. It is hardly surprising that control over Taxila was lost in the fifth century, while Achaemenid power in Central Asia came and went. In 499 the Greek cities of Ionia (western Anatolia), amongst which Miletus, Mytilene and Ephesus were the most notable, rebelled and appealed for help from Athens and Sparta, the leading cities of what we would now call the Greek mainland. This revolt was crushed by 494, but Persian pride had been offended by the burning of its regional capital at Sardis, and a forward party of the Persian nobles, amongst them Mardonios, an important member of the imperial family, demanded the conquest of Greece. By 479 this had failed. Astonishingly, the Greeks had fought off an attack by the greatest military power in the world. This was an extraordinary military event which demands explanation.
Once the revolt of the Ionian cities had been put down in 494, the Persians were determined to punish Athens and Sparta for their support of the rebels. This began a series of wars which transformed the cities of Greece and their methods of waging war. In 492 Darius I (522–486 BC) sent a fleet against Greece, but it was destroyed by a sudden storm in the Aegean. In 490 the Persians came again, with every hope of victory. The Ionian Greeks were subdued, and the kingdoms of Balkan Greece, Thessaly and Macedonia had come to terms with Persia, opening the route into Greece from Anatolia. Sparta was a highly authoritarian state whose elite distrusted the relatively popular regime in Athens, while even within that city elitist factions were perfectly prepared to welcome a Persian intervention which would restore them to power. The Persian force gathered in Cilicia and sailed directly to Greece in a fleet of perhaps 400 merchantmen and 200 warships. They captured the city of Eretria on the island of Euboea which was an ally of Athens, and treated its population with great brutality.
Under the guidance of an Athenian called Hippias they then landed in the north of the plain of Marathon where their fleet could be safely beached. Their 1,000 horsemen dominated the open terrain of the plain of Marathon because the Athenians had no cavalry to oppose them. The Persian force was essentially the army of Anatolia, mainly archers and light infantry, reinforced by marines and perhaps some Iranian garrison forces. The quality of their infantry was, therefore, uneven, but so probably was that of the Athenians. Athens mobilised every man possible, including slaves, and this must have produced very variably equipped and trained soldiers. They were supported by 600–1,000 men from the small city of Plataea. It would seem that each side had about 25,000 men. This parity in part explains why nothing happened for four days (7–11 August) after the arrival of the Athenians. Both sides had good reasons for inaction. The Persians would not have wanted to assault the strong Athenian position across the narrow southern end of the plain, and in any case they were anticipating that the pro-Persian party in Athens would open the gates of the city. The Athenians hoped the Spartans would arrive – they had refused to come until the full moon because of a religious festival. The Athenians dared not advance across the open plain where the strong enemy cavalry force would have cut them to pieces. In any case time was on their side because the Persians were very distant from their bases and were bound to run out of supplies.
This stand-off ended on 11 August when the Persians suddenly re-embarked their cavalry and sailed for Athens, presumably hoping to precipitate a coup in the city by their very appearance. It was a bold move, but it meant that the Persian infantry guarding the ships were now outnumbered. Miltiades, the seasoned Athenian commander, saw his opportunity and as soon as the Persian ships had gone he ordered an attack – he and the war party needed a victory if they were to hold the line against their pro-Persian enemies in Athens. According to Herodotus:
When the Persians saw the Athenians running towards them, they got ready to receive them, but they thought the Athenians must be mad – mad enough to bring about their utter destruction – because they could see how few of them there were, and that their charge was unsupported by either cavalry or archers.
The sudden Athenian advance seems to have surprised the Persian infantry whose best troops were in the centre of their line. What followed was a real soldiers’ fight because the Athenians lost all formation as they raced towards the enemy. Herodotus says that the two armies were 8 stades (about 1.25 kilometres) apart. No force, let alone the scratch Greek troops, could maintain formation at the run over such a distance. Herodotus says that this running attack was entirely novel in the Greek experience, and it would certainly have been disastrous if the Persian cavalry had been present because they would have outflanked the disordered infantry. But the Persian cavalry had gone and the wild advance had the enormous advantage of momentum once it had passed through the arrows of the Persian archers, because the defenders seem to have built no field fortifications. As the Athenian troops, arriving in small units piecemeal, crashed into the Persians a savage hacking match developed. Herodotus says that ‘the fighting at Marathon was long and drawn out’. At first the Persian centre drove back the Athenians, but the lighter forces on their flanks were defeated by the Plataeans on the left and the Athenians on the right, and these forces then turned on the enemy centre and cut it to pieces, killing 6,400 for a loss of only 192. But the Greeks were unable to follow up their victory because they needed to hasten back to Athens to prevent a pro-Persian coup, so the Persians got away in their fleet, losing only seven ships.
It is sometimes thought that Miltiades deliberately weakened his centre to draw the Persian strength into an advance, but it seems very unlikely that any general could have exerted much control in these circumstances or that such a scratch army could have manoeuvred in this way. Miltiades had been chosen as commander of the Athenians because he was familiar with Persian ways, and he deserves great credit for seizing the opportunity presented by the departure of the Persian cavalry. In essence the Athenians won because the Persians divided their own forces and sent away their best troops in the cavalry. Moreover, those left behind were lax in preparing their defence, particularly as they were outnumbered. The Greeks probably fought with great determination and desperation in the face of an enemy whose ruthlessness had been clearly demonstrated by the brutal treatment of Eretria. This was not a victory for the phalanx, because the Athenians must have arrived in loose and extended formations, but the rout of the Persian light infantry by the Athenians whose ranks included the more heavily equipped hoplites was an important indicator for the future.