The rise of the Athenian Empire was a direct continuation of the conflict with Persia. It's impossible to understand the Peloponnesian War without taking into account the role Persia played in backing the eventual winners. In fact, for Cyrus the Younger, the youthful son of Darius II and satrap of the western provinces, the Peloponnesian War was merely a means to an end. Supporting Sparta was Cyrus' path to accumulating the allies and prestige he would eventually need to take his father's throne. For him, the whole apocalyptic conflict was an adjunct to the succession struggle within the Persian Empire. When Cyrus eventually marched on the center of the empire after his father's death, he did so with an army of Greek mercenaries, Xenophon among them. There was no sharp break between Persian involvement in the Peloponnesian War, Cyrus' rebellion against his brother, and what came afterward in the 70 years between those events and Alexander's invasion of Asia Minor. This was now a deeply and irrevocably intertwined political world. Just seven years after the alliance between Persia and Sparta won the Peloponnesian War, the Spartans invaded Persian territory in Asia. The Persians retaliated by spending immense amounts of money to buy friends in Greek Pelaes, Athens included, to form an anti-Spartan alliance. The great king even served as the guarantor of the eventual peace settlement between the Greek police, perhaps a preview of the role Philip would eventually carve out for himself with the League of Corinth. This pattern of Persian involvement with Greek politics, supporting factions within cities and some cities against others, was a constant all the way up until the eve of the Macedonian invasion. As part of this relationship, which both Greeks and Persians cultivated for their own reasons, Greek soldiers often went east while Persian gold went west. This only grew more intense over the course of the 4th century BC as internal conflicts within the Persian Empire threatened to tear the realm apart. Artaxerxes II defeated Cyrus the Younger in 401 BC and was actually the longest reigning king of his dynasty. He didn't die until 359 BC. But his reign was filled with unrest. Egypt rebelled at the very beginning of his reign and was lost despite multiple attempts to recover the rich province. A group of western satraps launched a rebellion between 372 and 362 BC that took an entire decade to put down. All of these conflicts, seemingly internal to the Persian Empire, involved Greeks in some way. Individual Greeks fought for the great king and his rebellious subjects, and contingents of Greek soldiers filled the armies of Egyptian pharaohs and Persian satraps alike. Many scholars have argued that the Greeks were the most important force within the armies that were fighting over Persia throughout the 4th century BC, a product of their raw battlefield superiority and professionalism. One Persian hired Greeks, so the others had to hire Greeks too if they wanted to win, meaning that Greeks often fought each other in Persian service. From that perspective, the eventual Macedonian conquest of Persia simply built upon an existing military superiority. It's common to call these Greeks mercenaries in the sense that they were professional soldiers who fought for money without particular allegiance to their employers. A recent book by the historian Geoffrey Ropp has made some really forceful arguments against the prevailing view of Greeks fighting in the East, though. The Greek way of war wasn't fundamentally superior, Ropp argues. This view is instead the product of a historical tradition that was deeply hostile to the Persians, and so distorted the reality with a series of literary tropes and exaggerations. Whenever we can see the actual composition of a Persian army in this period, Greeks never made up more than a large minority of the troops involved in any given campaign. People who had actually fought in Persia, Xenophon included, had no illusions about the effectiveness of the great king's many other soldiers. Greeks were hardly invincible battlefield demigods towering over the dross of Persia. It was only much later Greek and Roman historians who became convinced of Persia's military inferiority, centuries removed from the events in question. Persians were perfectly good fighters, as were the many other subject peoples of the Persian Empire. The Greeks had no monopoly on military skills. But there were a lot of Greeks. They were near the western provinces of the Persian Empire, where unrest was most common, and their services were available. And yet they weren't solely fighting for pay as individuals recruited in an open market. Ropp argues that calling the many Greeks who did fight in the East simple mercenaries misses the basic political dynamics that drew them there. They may have been paid, but rather than being free agents, a great many of them were allies of the Persian parties they were fighting for. Their home police had sent them, or arranged for them to be sent, as contingents of soldiers serving the needs of their state in a formal or informal international alliance. Professional soldiers they may have been, but pure mercenaries they were not. For what it's worth, very few pure mercenaries have ever existed in history, even during the mercenary heyday of the 14th to 17th centuries. Even then, there were still long-term relationships, political concerns, and structures that dictated who fought for whom, not just pure monetary gain or the open hand of the market. In this sense, then, the Greeks of the 4th century BC who fought in Persia were very much in line with that norm. The of Greek soldiers had value. Both Greek pilais and Persian satraps or kings knew this. As those parties were bargaining with each other, Greeks and Persians, the provision of soldiers was the currency that Greek pilais could provide in return for Persian support. This was the military and political context that first Philip and then Alexander stepped into, one in which the Persians were perfectly aware of the internal dynamics of the Greek world, including the rise of Macedonia and the threat it posed. The Greeks, too, were aware of the inner workings of the Persian Empire thanks to generations of intensive interaction and the back-and travel of thousands of Greeks into Persian territory. What the Greeks were not was inherently superior, either culturally or militarily. What Alexander eventually did couldn't have been accomplished by any other Greek general just because that general was also part of the Greek world, whatever that means. Now, that doesn't mean that everything was perfectly well inside the Persian Empire. Scholars used to believe that the great king's realm was in steady decline throughout the 4th century BC, making it ripe for conquest when Alexander invaded. But that's no longer the prevailing view. When we look at archaeological evidence and texts from within Persia rather than hostile Greek accounts, there's an argument to be made that the empire was actually getting stronger. Artaxerxes II had spent much of his 45-year reign putting down rebellions and uprisings, but that was kind of baked into the DNA of the Persian Empire. It was quite decentralized by nature, and ambition on the fringes could easily turn into open warfare. Artaxerxes II's son, Artaxerxes III, followed him onto the throne without incident in 359 BC, and his reign followed the same pattern of drawn-out internal conflicts that were eventually quelled. Artaxerxes III even succeeded in recovering the lost province of Egypt in the late 340s BC. He was not a popular king, however, and our Greek sources paint Artaxerxes III as a brutal man. How much of the specifics of their account we should believe is hard to say, but they do tell us that he was poisoned by one of his high officials in 338 BC, and that few tears were shed. Unfortunately, we know very little about the reign of his successor, Darius III, who was defined almost entirely by his eventual defeat at the hands of Alexander the Great. Our available sources are extraordinarily biased, painting Darius as incompetent, cowardly, and unfit to rule the Persian Empire. He needed to be unfit so that Alexander could be fit in those accounts. But we don't have to believe any of that. In fact, the first four years of Darius' rule seem to have been quite successful, especially considering the growing Macedonian threat in the western provinces. The early successes of the expeditionary force under Parmenio's command gave way to a string of defeats and a coherent counteroffensive led by Darius' picked subordinates. But Darius III was not Alexander. The Macedonian king's vision for his campaign was extraordinarily ambitious from the very beginning. When he first crossed the Hellespont into Asia in the spring of 334 BC, his first stop was the site of Troy, where he sacrificed at the tombs of Achilles and Priam. The Temple of Athena in Troy held a set of arms and armor that were believed to be those of Achilles, and after making a sacrifice, Alexander swapped his own shield for that of Achilles. The message was not a subtle one. Alexander was placing himself in the tradition of the great heroes of bygone days. But despite those heroic pretensions, Alexander was still confronting a quite difficult military situation. Liberating the Greek cities of the Anatolian coastline was all well and good, but making them pay for the cost of his campaigning would soon wear out his welcome and drive them back into the arms of the great king. The army had not brought an abundance of provisions from Europe, and spreading out to forage across the countryside would limit their ability to concentrate for a decisive battle. Alexander had to seek out the Persian armies in Asia Minor and bring them to grips as quickly as possible. He found them waiting for him on the eastern bank of the Granicus River, just south of the Sea of Marmara, the enclosed body of water separating Europe and Asia with Byzantium on its northern side. The Persian forces occupied a strong defensive position. Their intention was obviously to keep Alexander bottled up in the far west of the Persian Empire, exhausting his supplies and the patience of his allies. Time was on their side. One of the Persian commanders, a Greek from Rhodes named Memnon, suggested laying waste to the nearby territory to deprive the Macedonians of supplies. The Persian commander, whose satrapy this was, rejected the idea and wanted to force a battle. Their army was almost certainly smaller than Alexander's, but their position was perfect for defense. The Granicus wasn't especially wide, but its waters ran quickly and its banks were 8-12 feet high, covered in scrub and trees.