The ancestors of the Persians settled in Persis in the end of the third millennium BC. They were peaceful shepherds, who moved up to the mountains and then down to the valleys depending on the season. For many generations the life in Persis continued in this way; it was shacked with the whole of the Middle East by the Assyrian casualties. The Assyrian military wiped out the kingdom of Elam, to whom the Persians were vassals, leaving the capital Susa to the lizards. Their rule was not long, though. In 612 BC the Assyrian Empire was destroyed by the Medes and Babylonians, who shared its vast territories. Subsequently, the Persians became subject to the Median Empire. The ties with the latter were very strong, however, not only because the two peoples were of the same origin, but also in the way of a political marriage. The daughter of the Median king Astyages (585/584 - 550), Mandane, was married to the ruler of Persis, a certain Cambyzes, "a decent peaceful man" of the Achaemenid dynasty. They soon had a song, who was called Kurush (we know him by the Greek version of his name, which is Cyrus). Many legends surround the birth of Cyrus. According to one of them, Astyages once dreamt that from his daughter's womb came out a great vine, which spread itself throughout the whole of Asia. The Magi interpreted this dream by saying that Mandane would give birth to a child, whom will conquer the continent. The worried Astyages took the baby and gave it to one of his subjects, Harpagus, with orders to murder it. Harpagus, however, did not want to kill an infant so lively and handsome, so he gave it to some shepherd, who brought it up as his own son. When Astyages learnt about that in a few years, he punished Harpagus in a demonic way. He boiled his son and fed him with it without telling him what he was eating. The poor father understood he had eaten his own son only when the servants brought to him a dish with the head of the boy. After that Astyages sent the young Cyrus to his parents in Persis.

Meanwhile Astyages' own reign became more and more horrific, and the people grew restless. This opposition was led, for obvious reasons, by Harpagus. He persuaded the Magi to join his cause and then sent a letter to Cyrus, saying that if he were to attack his grandfather, the Median army would not fight him. When Astyages learnt of his grandson's intentions, he send an army against it and so blinded was he, that he appointed Harpagus as its leader! The two opposing forces met on a murky afternoon near the old Persian capital of Pasargadae, but before a single arrow was shot, most of the Medes deserted to the Persians. Cyrus then proceeded to capture Astyages in Ecbatana (the Median capital), but contrary to the custom of the times, spared his life. After that he assumed the rulership of the Median Empire. With it came the administration system which he left as it was, not changing a thing (550 BC). Cyrus was a very tolerant ruler, who recognized the local customs and appreciated them wherever he went.

In Asia Minor the border between the Median and the Lydian empires had been set at the River Halys. Seeing that the Empire of the Medes had been overthrown by some unknown Persian prince, the Lydian king Croesus sought to expand his empire at the expense of his young neighbour and in 547 marched into Median territory and was met by the Medo-Persian forces of Cyrus. In the battle that followed, both sides suffered heavy casualties, but Croesus thought he was losing and withdrew to Sardis for the winter. Cyrus, however, was not planning to wait for spring to come. He followed Croesus and arrived so quickly at Sardis, that according to Herodotus "was his own herald". Croesus gathered his army and sent it against the Persians. The mighty Lydian cavalrymen with their lethal spears rode in the front and attacked. They withdrew at once, though, because Cyrus had used a very shrewd tactic. He had mounted his men on camels, the smell of which scared the horses. The rest of the Lydian army was then defeated. Croesus prepared himself for a long siege, summoning his allies in the meantime. The heavily-fortified Lydian capital fell within two weeks. Croesus became one of Cyrus' advisors. The Persian then returned to Ecbatana, sending Harpagus to conquer the Ionian Greeks of Asia. After having conquered Media and Lydia, Cyrus turned his attention further to the north, defeating the various barbaric tribes on his way. He crossed the Oxus river; at the next river, though, the Jaxartes, he stopped, making it his north frontier.

In the south, the biggest metropolis of the Ancient World, Babylon, was still independent, though almost surrounded by Persian territory. In 541 Cyrus decided to attack it. The Opis River slowed down his march, however, and it was only in the spring of 539 that he crossed it and defeated the Babylonian army there. Herodotus then gives a lengthy account on a prolonged siege of Babylon. Other sources state that on his way to the city, Cyrus was met by a Babylonian commander, Gobrius, who offered him the surrender of the city. The Persian accepted it, and Gobrius went back and opened the gates for the victor, who was met by the population amidst wild rejoicing. Cyrus was crowned King of Babylon and prayed to the Babylonian gods.

The next objective of Cyrus was Egypt. He was preparing his army to attack it, when news came that the Scythian tribe Massagaeti was raiding Persian territory between the Caspian and Aral Sea. He hurried north to meet the warrior-queen Tomyris. Herodotus states that this was one of the most hard-fought battles in history. The Scythians eventually gained the upper hand, but the Persians refused to flee. In that battle, Cyrus was slain, along with the better half of his army (530). His body was carried back to Pasargadae, the place of his first triumph, and was buried thence. Alexander the Great came to visit Cyrus' tomb 200 years later.

Cyrus was succeeded by his son Cambyzes. As a satrap of Babylonia, Cambyzes had become a good administrator. Now he took on his father's ideas for conquest. In 525 he attacked Egypt, won the Battle of Pelusium and marched into the Nile Delta. In the beginning he was as tolerant as Cyrus, and had himself proclaimed pharaoh. But when he sought to expand his African possessions, various misfortunes faced him. First he intended to attack Carthage, but the Phoenicians in his navy refused to fight their relatives. Then Cambyzes sent troops to some oasis in Amon (actually the infamous Siwah, later visited by Alexander), but they got lost in a sand storm and died. Lastly, he intended to subdue Nubia, but his weary hungry troops never reached the capital of Meroe. When news of cannibalism among the soldiers reached Cambyzes, the startled king ordered retreat. After such casualties, the Great King started showing serious signs of insanity. Once he beat his pregnant wife to death. When rumours of a rebellion came to him, Cambyzes hurried home. He died on the way from a wound he had given himself, according to some historians (522). It is said that "Cyrus was the father of the Empire, Cambyzes was its Tyrant, and Darius was its economist". Cambyzes, however, was probably not as bad as they tried to make him.

In the civil war that followed Cambyzes' death, Darius, the son of Histaspes the satrap of Parthia and Hyrcania and also of the Achaemenid synary, won the throne. According to Herodotus, before his final battle with the Massagaeti, Cyrus saw in a dream the son of Histaspes with wings, one of which shaded Europe and the other Asia. After Darius became king, he had to put down various rebellions, which took him more than a year. Finally in 521 he assumed utter control. Similarly to Cyrus, Darius was an excellent warrior. But more so he was a brilliant administrator. He built the 1200-km Royal Highway which linked Sardis with the Imperial capital Susa. He greatly improved the three Persian capitals at the time - Pasargadae, Susa and Ecbatana. But Darius wanted a city that would suit his own taste. Consequently he started building Persepolis - the magnificent ceremonial capital of the Empire, where each year the vassal peoples would come to offer their tributes to the Great King, the King of Kings and ruler of the world. The city was finished and improved by Darius' son, Xerxes.

Darius was also permanently on a march with the army. In 517 he conquered North-western India with Punjab, which became the 21st satrapy of the Persian Empire. Of all the provinces, India supplied by far the biggest annual tribute (10 tons of gold powder. In comparison Babylon sent 30 tons of silver). In 513 Darius led the first Asiatic expansion into Europe. His plans were to conquer Scythia and control the trade roots west. Macedonia obeyed, and Darius marched his army through Thrace. The Scythians, however, were something else. Each time the Persians attacked them, they would fire a cloud of arrows from their horses and retreat. This way of fighting was devastating to the slow Persian army. Restless, Darius had to retreat south of the Danube. But he left the imperial presence in Thrace and Macedonia, right next to Greece. As for the Scythians, the Persians would never again try to subdue them. Instead they hired Scythian archers to train the Persian ones. The barbarians had ruthlessly hindered imperial expansion north of the rivers Jaxartes and Danube by slaying the best Persian king ever and successfully confronting his great descendant. This way of fighting, which later became known as "Parthian tactics", won out against Persians, Romans, and Greeks. The latter meanwhile had become a factor, which even the Great King of Persia must not neglect; pretty soon Darius the Great and his heirs would learn that.