Around 535 BCE, the Persian king Cyrus the Great initiated a protracted campaign to absorb parts of India into his nascent Achaemenid Empire.

[1] In this initial incursion, the Persian army annexed a large region to the west of the Indus River, consolidating the early eastern borders of their new realm.

With a brief pause after Cyrus' death around 530 BCE, the campaign continued under Darius the Great, who began to re-conquer former provinces and further expand the Achaemenid Empire's political boundaries.

Around 518 BCE, the Persian army pushed further into India to initiate a second period of conquest by annexing regions up to the Jhelum River in what is today known as Punjab.

Persian penetration into the Indian subcontinent occurred in multiple stages, beginning from the northern parts of the Indus River and moving southward.

[7] As mentioned in several Achaemenid-era inscriptions, the Indus Valley was formally incorporated into the Persian realm through provincial divisions: Gandāra, Hindush, and Sattagydia.

Persian rule over the Indus Valley decreased over successive rulers and formally ended with the Greek conquest of Persia, led by Alexander the Great.

Finally, the Achaemenid Empire underwent a considerable expansion, both east and west, during the reign of Cyrus the Great (c.600–530 BC), leading the dynasty to take a direct interest into the region of northwestern India.

Herodotus gives a full list of the ethnicities of the Achaemenid army, in which are included Bactrians, Sakas (Scythians), Parthians, Sogdians,[27] Ionians (Greeks), Egyptians, Ethiopians, etc.

The Greek Scylax of Caryanda, who had been appointed by Darius I to explore the Indian Ocean from the mouth of the Indus to Suez left an account, the Periplous, of which fragments from secondary sources have survived.

The 'DB' Behistun inscription[30] of Darius I (circa 510 BCE) mentions Gandara (𐎥𐎭𐎠𐎼, Gadāra) and the adjacent territory of Sattagydia (𐎰𐎫𐎦𐎢𐏁, Thataguš) as part of the Achaemenid Empire: King Darius says: These are the countries which are subject unto me, and by the grace of Ahuramazda I became king of them: Persia [Pârsa], Elam [Ûvja], Babylonia [Bâbiruš], Assyria [Athurâ], Arabia [Arabâya], Egypt [Mudrâya], the countries by the Sea, Lydia [Sparda], the Greeks [Yauna (Ionia)], Media [Mâda], Armenia [Armina], Cappadocia [Katpatuka], Parthia [Parthava], Drangiana [Zraka], Aria [Haraiva], Chorasmia [Uvârazmîy], Bactria [Bâxtriš], Sogdia [Suguda], Gandara [Gadāra], Scythia [Saka], Sattagydia [Thataguš], Arachosia [Harauvatiš] and Maka [Maka]; twenty-three lands in all.From the dating of the Behistun inscription, it is possible to infer that the Achaemenids first conquered the areas of Gandara and Sattagydia circa 518 BCE.

[33][29] Four identical foundation tablets of gold and silver, found in two deposition boxes in the foundations of the Apadana Palace, also contained an inscription by Darius I in Old Persian cuneiform, which describes the extent of his Empire in broad geographical terms, from the Indus valley in the east to Lydia in the west, and from the Scythians beyond Sogdia in the north, to the African Kingdom of Kush in the south.

[29] The DNa inscription[19] on Darius' tomb at Naqsh-i-Rustam near Persepolis records Gadāra (Gandāra) along with Hiduš and Thataguš (Sattagydia) in the list of satrapies.

[41] King Darius says: By the favor of Ahuramazda these are the countries which I seized outside of Persia; I ruled over them; they bore tribute to me; they did what was said to them by me; they held my law firmly; Media, Elam, Parthia, Aria, Bactria, Sogdia, Chorasmia, Drangiana, Arachosia, Sattagydia, Gandara (Gadāra), India (Hiduš), the haoma-drinking Scythians, the Scythians with pointed caps, Babylonia, Assyria, Arabia, Egypt, Armenia, Cappadocia, Lydia, the Greeks (Yauna), the Scythians across the sea (Sakâ), Thrace, the petasos-wearing Greeks [Yaunâ], the Libyans, the Nubians, the men of Maka and the Carians.The extent of Achaemenid territories is also affirmed by Strabo in his "Geography" (Book XV), describing the Persian holdings along the Indus:[44] The geographical position of the tribes is as follows: along the Indus are the Paropamisadae, above whom lies the Paropamisus mountain: then, towards the south, the Arachoti: then next, towards the south, the Gedroseni, with the other tribes that occupy the seaboard; and the Indus lies, latitudinally, alongside all these places; and of these places, in part, some that lie along the Indus are held by Indians, although they formerly belonged to the Persians.The nature of the administration under the Achaemenids is uncertain.

They fought in the last stages of the war, took part in the Destruction of Athens, but were finally vanquished at the Battle of Plataea:[84] Mardonius there chose out first all the Persians called Immortals, save only Hydarnes their general, who said that he would not quit the king's person; and next, the Persian cuirassiers, and the thousand horse, and the Medes and Sacae and Bactrians and Indians, alike their footmen and the rest of the horsemen.

Thereby the whole number, with the horsemen, grew to three hundred thousand men.At the final Battle of Plataea in 479 BCE, Indians formed one of the main corps of Achaemenid troops (one of "the greatest of the nations").

The hoard contained a tetradrachm minted in Athens circa 500/490-485/0 BCE, typically used as a currency for trade in the Achaemenid Empire, together with a number of local types as well as silver cast ingots.

[111][112][113] As reported by Strabo (XV, 1, 62),[114] when Alexander the Great was in Taxila, one of his companions named Aristobulus, noticed that in the city the dead were being fed to the vultures, a clear allusion to the presence of Zoroastrianism.

The Mudrarakshasa states that after Alexander's death, an alliance of "Shaka-Yavana-Kamboja-Parasika-Bahlika" was used by Chandragupta Maurya in his campaign to take the throne in Magadha and found the Mauryan Empire.

[128][130][127] David Brainard Spooner theorized upon Chandragupta Maurya's conquest and claimed that "it was with largely the Persian army that he won the throne of India.

"[129] Astronomical and astrological knowledge was also probably transmitted to India from Babylon during the 5th century BCE as a consequence of the Achaemenid presence in the sub-continent.

"[133]Various Indian artefacts tend to suggest some Perso-Hellenistic artistic influence in India, mainly felt during the time of the Mauryan Empire.

[144] The Lycian tombs, dated to the 4th century BCE, are either free-standing or rock-cut barrel-vaulted sarcophagi, placed on a high base, with architectural features carved in stone to imitate wooden structures.

[154] The Indian Kharosthi script shows a clear dependency on the Aramaic alphabet but with extensive modifications to support the sounds found in Indic languages.

[162] Some relatively high quality terracotta statuettes have been recovered from the Mauryan Empire strata in the excavations of Mathura in northern India.

[170] Several of these seem to represent foreign soldiers who visited India during the Mauryan period and influenced modellers in Mathura with their peculiar ethnic features and uniforms.

[172] One of the terracotta statuettes, a man nicknamed the "Persian nobleman" and dated to the 2nd century BCE, can be seen wearing a coat, scarf, trousers and a turban.

This elite was West Asian, specifically related to the Pahlavas and Sakas based in Iran and Afghanistan, and their presence was a consequence of their eastern forays into India.

Who while boldly penetrating into the remoter districts of upper India, came to a certain woody retreat, of which with its tranquil silence the Brahmans, men of sublime genius, were the possessors.

From their teaching he learnt the principles of the motion of the world and of the stars, and the pure rites of sacrifice, as far as he could; and of what he learnt he infused some portion into the minds of the Magi, which they have handed down by tradition to later ages, each instructing his own children, and adding to it their own system of divination".In ancient sources, Hystapes is sometimes considered as identical with Vishtaspa (the Avestan and Old Persian name for Hystapes), an early patron of Zoroaster.