Second Persian invasion of Greece

The second Persian invasion of Greece occurred during the Greco-Persian Wars, as King Xerxes I of Persia sought to conquer all of Greece. The invasion was a direct, if delayed, response to the defeat of the first Persian invasion of Greece at the Battle of Marathon, which ended Darius I's attempts to subjugate Greece. After Darius's death, his son Xerxes spent several years planning for the second invasion, mustering an enormous army and navy. The Athenians and Spartans led the Greek resistance. About a tenth of the Greek city-states joined the 'Allied' effort; most remained neutral or submitted to Xerxes.
The invasion began in spring 480 BC, when the Persian army crossed the Hellespont and marched through Thrace and Macedon to Thessaly. The Persian advance was blocked at the pass of Thermopylae by a small Allied force under King Leonidas I of Sparta; simultaneously, the Persian fleet was blocked by an Allied fleet at the straits of Artemisium. At the famous Battle of Thermopylae, the Allied army held back the Persian army for three days, before they were outflanked by a mountain path and the Allied rearguard was trapped and annihilated. The Allied fleet had also withstood two days of Persian attacks at the Battle of Artemisium, but when news reached them of the disaster at Thermopylae, they withdrew to Salamis.
After Thermopylae, all of Euboea, Phocis, Boeotia and Attica fell to the Persian army, which captured and burnt Athens. However, a larger Allied army fortified the narrow Isthmus of Corinth, protecting the Peloponnesus from Persian conquest. Both sides thus sought a naval victory that might decisively alter the course of the war. The Athenian general Themistocles succeeded in luring the Persian navy into the narrow Straits of Salamis, where the huge number of Persian ships became disorganised, and were soundly beaten by the Allied fleet. The Allied victory at Salamis prevented a quick conclusion to the invasion, and fearing becoming trapped in Europe, Xerxes retreated to Asia leaving his general Mardonius to finish the conquest with the elite of the army.
The following spring, the Allies assembled the largest ever hoplite army and marched north from the Isthmus to confront Mardonius. At the ensuing Battle of Plataea, the Greek infantry again proved its superiority, inflicting a severe defeat on the Persians and killing Mardonius in the process. On the same day, across the Aegean Sea an Allied navy destroyed the remnants of the Persian navy at the Battle of Mycale. With this double defeat, the invasion was ended, and Persian power in the Aegean severely dented. The Greeks would now move to the offensive, eventually expelling the Persians from Greece, the Aegean Islands and Ionia before the war finally came to an end in 449 BC with the Peace of Callias.

Background

The Greek city-states of Athens and Eretria had supported the unsuccessful Ionian Revolt against the Persian Empire of Darius I in 499–494 BC. The Persian Empire was still relatively young and prone to revolts among its subject peoples. Moreover, Darius was a usurper and had spent considerable time extinguishing revolts against his rule. The Ionian revolt threatened the integrity of his empire, and Darius thus vowed to punish those involved. Darius also saw the opportunity to expand his empire into the fractious world of Ancient Greece. A preliminary expedition under Mardonius, in 492 BC, to secure the land approaches to Greece ended with the re-conquest of Thrace and forced Macedon to become a fully subordinate kingdom part of Persia. It had previously been a vassal as early as the late 6th century BC, but remained having autonomy and was not fully subordinate yet.
In 491 BC, Darius sent emissaries to all the Greek city-states, asking for a gift of "earth and water" in token of their submission to him. Having had a demonstration of his power the previous year, the majority of Greek cities duly obliged. In Athens, however, the ambassadors were put on trial and then executed; in Sparta, they were simply thrown down a well. This meant that Sparta was also now effectively at war with Persia.
Darius thus put together an ambitious task force under Datis and Artaphernes in 490 BC, which attacked Naxos, before receiving the submission of the other Cycladic Islands. The task force then moved on Eretria, which it besieged and destroyed. Finally, it moved to attack Athens, landing at the bay of Marathon, where it was met by a heavily outnumbered Athenian army. At the ensuing Battle of Marathon, the Athenians won a remarkable victory, which resulted in the withdrawal of the Persian army to Asia.
Darius therefore began raising a huge new army with which he meant to completely subjugate Greece; however, in 486 BC, his Egyptian subjects revolted, indefinitely postponing any Greek expedition. Darius then died while preparing to march on Egypt, and the throne of Persia passed to his son Xerxes I. Xerxes crushed the Egyptian revolt, and very quickly restarted the preparations for the invasion of Greece.

Persian preparations

Since this was to be a full-scale invasion, it required long-term planning, stock-piling and conscription. It was decided that Xerxes' Pontoon Bridges were to be set up to allow his army to cross the Hellespont to Europe, and that a canal should be dug across the isthmus of Mount Athos. These were both feats of exceptional ambition, which would have been beyond any contemporary state. However, the campaign was delayed one year because of another revolt in Egypt and Babylonia.
In 481 BC, after roughly four years of preparation, Xerxes began to muster the troops for the invasion of Europe. Herodotus gives the names of 46 nations from which troops were drafted. The Persian army was gathered in Asia Minor in the summer and autumn of 481 BC. The armies from the Eastern satrapies was gathered in Kritala, Cappadocia and were led by Xerxes to Sardis where they passed the winter. Early in spring it moved to Abydos where it was joined with the armies of the western satrapies. Then the army that Xerxes had mustered marched towards Europe, crossing the Hellespont on two pontoon bridges.

Size of the Persian forces

The numbers of troops that Xerxes mustered for the second invasion of Greece have been the subject of endless dispute because the numbers given in ancient sources are very large indeed. Herodotus claimed that there were, in total, 2.5 million military personnel, accompanied by an equivalent number of support personnel. The poet Simonides, who was a contemporary, talks of four million; Ctesias, based on Persian records, gave 800,000 as the total number of the army that was assembled by Xerxes. While it has been suggested that Herodotus or his sources had access to official Persian Empire records of the forces involved in the expedition, modern scholars tend to reject these figures based on knowledge of the Persian military systems, their logistical capabilities, the Greek countryside, and supplies available along the army's route.
Modern scholars thus generally attribute the numbers given in the ancient sources to the result of miscalculations or exaggerations on the part of the victors, or disinformation by the Persians in the run up to the war. The topic has been hotly debated but the modern consensus revolves around the figure of 200,000 or 300,000–500,000. Nevertheless, whatever the real numbers were, it is clear that Xerxes was eager to ensure a successful expedition by mustering overwhelming numerical superiority by land and by sea, and also that much of the army died of starvation and disease, never returning to Asia.
Herodotus tells us that the army and navy, while moving through Thrace, was halted at Doriskos for an inspection by Xerxes, and he recounts the numbers of troops found to be present:

Units	Numbers
1,207 triremes with 200-man crews from 12 ethnic groups: Phoenicians along with the "Syrians of Palestine", Egyptians, Cyprians, Cilicians, Pamphylians, Lycians, Dorians of Asia, Carians, Ionians, Aegean islanders, Aeolians, Greeks from Pontus	241,400
30 marines per triremefrom the Persians, Medes or Sacae	36,210
3,000 Galleys, including 50-oar penteconters, 30-oared ships, light galleys and heavy horse-transports	240,000^b
Total of ships' complements	517,610
Infantry from 47 ethnic groups, including Medes, Cissians, Hyrcanians, Assyrians, Chaldeans, Bactrians, Sacae, Indians, Arians, Parthians, Chorasmians, Sogdians, Gandarians, Dadicae, Caspians, Sarangae, Pactyes, Utians, Mycians, Paricanians, Arabians, Ethiopians of Africa, Ethiopians of Baluchistan, Libyans, Paphlagonians, Ligyes, Matieni, Mariandyni, Cappadocians, Phrygians, Armenians, Lydians, Mysians, Asian Thracians, Lasonii, Milyae, Moschi, Tibareni, Macrones, Mossynoeci, Mares, Colchians, Alarodians, Saspirians and Red Sea islanders.	1,700,000
Horse cavalry from the Persians, Sagartians, Medes, Cissians, Indians, Caspians and Paricanians.	80,000
Arab camel troops and Libyan charioteers	20,000
Total Asian land and sea forces	2,317,610
120 triremes with 200-man crews from the Greeks of Thrace and the islands near it.	24,000
Balkan infantry from 13 ethnic groups: European Thracians, Paeonians, Eordi, Bottiaei, Chalcidians, Brygians, Pierians, Macedonians, Perrhaebi, Enienes, Dolopes, Magnesians, Achaeans	300,000
Grand total	2,641,610

Herodotus doubles this number to account for support personnel and thus he reports that the whole army numbered 5,283,220 men. Other ancient sources give similarly large numbers. The poet Simonides, who was a near-contemporary, talks of four million; Ctesias gave 800,000 as the total number of the army that assembled in Doriskos.
An early and very influential modern historian, George Grote, set the tone by expressing incredulity at the numbers given by Herodotus: "To admit this overwhelming total, or anything near to it, is obviously impossible." Grote's main objection is the supply problem, though he does not analyse the problem in detail. He did not reject Herodotus's account altogether, citing the latter's reporting of the Persians' careful methods of accounting and their stockpiling of supply caches for three years, but drew attention to the contradictions in the ancient sources. A later influential historian, J. B. Bury, calls Herodotus's numbers "wholly fabulous" and judges that the Persian land forces may have been 180,000. A major limiting factor for the size of the Persian army, first suggested by Sir Frederick Maurice is the supply of water. Maurice suggested in the region of 200,000 men and 70,000 animals could have been supported by the rivers in that region of Greece. He further suggested that Herodotus may have confused the Persian terms for chiliarchy and myriarchy, leading to an exaggeration by a factor of ten. Other early modern scholars estimated that the land forces participating in the invasion at 100,000 soldiers or less, based on the logistical systems available to the Ancients.
Munro and Macan note Herodotus giving the names of six major commanders and 29 myriarchs ; this would give a land force of roughly 300,000 men. Other proponents of larger numbers suggest figures from 250,000 to 700,000.