It was not without some crusading zeal that he now set in motion the invasion of Greece. With the aid of Ahuramazda he would avenge his father’s defeat at the hands of the Greeks, and bring these dissident worshippers of false gods within the divine rule of Persia and its monarchy.

He had set out from Susa in the spring of 481. On 10 April of that year there had been an eclipse of the sun (Herodotus wrongly assigns this to the year 480). Not unnaturally, in view of the immensity of the preparations, and the fact that Darius himself had suffered defeat on a similar expedition, this eclipse caused considerable concern, if not consternation, in the court and among the people.

However, the Magi (the wise men who watched the stars and attended to religious rituals), primed with knowledge of the Universe that had been largely acquired from the absorption of Babylon into the Persian Empire, hastened to reassure the Great King. It is possible that, from the Babylonian astronomers, they had learned that the moon is the eclipsing body. Their explanation of the event was completely consistent with this. The sun, they said, symbolised the Greeks and the moon the Persians. The eclipse was not an ill omen therefore. It showed that the Greeks were destined to be overshadowed and conquered by the Persian moon.

Having spent the winter in Sardis, while all the contingents of his army assembled ready for their march north in the following spring, Xerxes could certainly reflect that he and his advisers, his ministers and his overseers of the various work-forces had done all that was possible to obviate any obstacles in their path. His invasion of Europe was so well planned that one is astonished at such efficiency and logistical preparation at such an early date. When one compares the inefficiency of the Crusades many centuries later, or even the relatively poor comprehension of the necessity for long-scale planning and forethought in major wars and campaigns right up to the twentieth century, one can only marvel at the organisation and bureaucratic competence of the Persian Empire. While the Greeks were inclined to see in the preparations made by Xerxes no more than that hubris or megalomania which they associated with all despots and Oriental monarchs, there is - to modern eyes - nothing to show that Xerxes and his staff were anything other than magnificent planners, on a scale undreamed of at that period in history.

The preparations for this massive expedition against their country had been known to the Greeks for years. It was not possible that they could have been kept secret, for they involved an immense task force, and works of so extravagant a nature that they almost rivalled the building of the Pyramids. First of all, Xerxes had no intention of allowing his fleet to be brought to ruin off the stormy peninsula of Mount Athos - as had happened to the fleet of Darius during his invasion of Greece ten years previously. The expedition of Xerxes was four years in preparation, and one of the main projects was the digging of a canal through the isthmus of Mount Athos. The mountain, as Herodotus writes, ‘is very well-known and high and stands out into the sea. It is inhabited, and on the landward side where the heights end there is a kind of isthmus roughly a mile and a half wide. All of this is level land or small hillocks…. The inhabitants [of the mountain] Xerxes now intended to turn into islanders.’

He goes on to describe how the canal through the low land was cut. Conscripted Greeks from the neighbouring areas were used for much of the labour, while skilled workmen were also brought over from Asia Minor. Outstanding among them were the Phoenicians (one of the most technologically advanced people of that era, and the nation which also formed the backbone of the Persian fleet). Herodotus makes the comment that, while the other ‘nations’ engaged on the task of digging the canal had constant trouble with landslips, caused by the fact that they dug their part of the canal like a simple ditch with straight sides, only the Phoenicians realised that the digging must be much wider at the top in order to leave what engineers call an ‘angle of rest’. (Centuries later similar difficulties had to be overcome during the digging of the Suez Canal.) ‘They proved their remarkable skill,’ he writes, ‘for, in the section that had been allotted to them, they dug a trench twice the width required for the canal itself when finished. Digging at a slope they narrowed it as they went further down so that at the bottom their section was as wide as the rest.’

Everything was provided for: there was the equivalent of a canteen for the workmen, with grain brought from the homeland, as well as a forum or meeting-place, and an open market - proof in itself that the workmen were paid in coin. Herodotus’ conclusion about the gigantic labour of the canal was that the whole thing was no more than yet another example of the ostentation of Xerxes. ‘There would not have been any difficulty’, he wrote, ‘in having the ships dragged across the isthmus on land, yet he gave orders for the canal to be made so wide that two warships could be rowed abreast [down its length].’ The historian was thinking, of course, of the practice at Corinth of dragging ships across the isthmus which connects northern Greece with the Peloponnese. His great mistake, however, was to equate the routine passage of merchantmen and warships between the Gulf of Patras and the Aegean Sea with the emergent movement of a large fleet into hostile waters. While waiting to take their turn for haulage overland, they might well have been overwhelmed by one of the sudden and violent storms that quite often afflict the Aegean.

Nothing was left to chance. Dumps of provisions, both for men and for their animals, were sited at regular intervals along the route that the Grand Army was to take. The Persians, unlike the Greeks, were not principally bread- or grain-eaters (as most Mediterranean peoples are to this day).