Around 535 BCE, the Persian king Cyrus the Great initiated a protracted campaign to absorb parts of northwestern South Asia into his nascent Achaemenid Empire. 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 present-day Punjab. At their peak, the Achaemenids incorporated and ruled much of modern-day Pakistan into their territory.

The first secure epigraphic evidence through the Behistun Inscription gives a date before or around 518 BCE. Persian penetration into the Indian subcontinent occurred in multiple stages, beginning from the northern parts of the Indus River and moving southward. 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 waned over succeeding centuries and formally ended with the Greek conquest of Persia, led by Alexander the Great, giving rise to independent kingdoms such as those of Abisares, Porus, and Taxiles, as well as a number of , which would later confront the Macedonian army as it massed into the region for Alexander's Indian campaign. The Achaemenid Empire set a precedence of governance through the use of satrapies, which was further implemented by the Macedonian Empire, the Indo-Scythians, and the Kushan Empire.

Achaemenid conquest

For millennia, the northwestern part of India had maintained some level of trade relations with the Near East. Finally, the Achaemenid Empire underwent a considerable expansion, both to the 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.

Cyrus the Great The conquest is often thought to have begun circa 535 BCE, during the time of Cyrus the Great (600–530 BCE). Cyrus probably went as far as the banks of the Indus River and organized the conquered territories under the satrapy of Gandāra (Old Persian cuneiform: 𐎥𐎭𐎠𐎼, Gadāra, also transliterated as Gandāra since the nasal "n" before consonants was omitted in the Old Persian script, and simplified as Gandara)Some sounds are omitted in the writing of Old Persian, and are shown with a raised letter (Old Persian p. 164, Old Persian p. 13). In particular Old Persian nasals such as "n" were omitted in writing before consonants (Old Persian p. 17, Old Persian p. 25). as inferred from the Behistun inscription. The province was also referred to as Paruparaesanna (Greek: Parapamisadae) in the Babylonian and Elamite versions of the Behistun inscription. The geographical extent of this province was wider than the Indian Gandhara.: "One should, therefore, be careful to distinguish the limited geographical unit of Gandhāra from the political one bearing the same name." Various accounts, such as those of Xenophon or Ctesias, who wrote Indica, also suggest that Cyrus conquered parts of India. Another Indian province was also conquered, named Sattagydia (𐎰𐎫𐎦𐎢𐏁, Thataguš) in the Behistun inscription. It was probably contiguous to Gandāra, but its actual location is uncertain. Fleming locates it between Arachosia and the middle Indus. Fleming also mentions Maka, in the area of Gedrosia, as one of the Indian satrapies.

Darius I A successor of Cyrus the Great, Darius I was back in 518 BCE. The date of 518 BCE is given by the Behistun inscription, and is also often the one given for the secure occupation of Gandāra in Punjab.Marshall, John (1975) . Taxila. Vol. I. Delhi: Motilal Banarsidass. p. 83. Darius I later conquered an additional province that he calls Hindush in his inscriptions (Old Persian cuneiform: 𐏃𐎡𐎯𐎢𐏁, H-i-du-u-š, also transliterated as Hindūš since the nasal "n" before consonants was omitted in the Old Persian script, and simplified as Hindush), corresponding to the Indus Valley. The Hamadan Gold and Silver Tablet inscription of Darius I also refers to his conquests in India.

The exact area of the province of Hindush is uncertain. Some scholars have described it as the middle and lower Indus Valley and the approximate region of modern Sindh,; ; but there is no known evidence of Achaemenid presence in this region, and deposits of gold, which Herodotus says was produced in vast quantities by this Province, are also unknown in the Indus delta region."The region was soon to appear as Hindūš in the Old Persian inscriptions... Transparent though the name appears at first sight, its location is not without problems. Foucher, Kent and many subsequent writers have identified Hindūš with its etymological equivalent, Sind, thereby placing it on the lower Indus towards the delta. However, (...) no material evidence of Achaemenid activity in this region is so far available. (...) There seems no evidence at present of gold production in the Indus delta, so this detail seems to weight against the location of the Hindūš province in Sind. (...) The alternative location to Sind for an Achaemenid province of Hindūš is naturally at Taxila and in the West Punjab, where there are indications that a Persian satrapy may have existed, though no clear evidence of its name." in Alternatively, Hindush may have been the region of Taxila and western Punjab, where there are indications that a Persian satrapy may have existed. There are few remains of Achaemenid presence in the east, but, according to Fleming, the archaeological site of Bhir Mound in Taxila remains the "most plausible candidate for the capital of Achaemenid India", based on the fact that numerous pottery styles similar to those of the Achaemenids in the East have been found there, and that "there are no other sites in the region with Bhir Mound's potential".

According to Herodotus, Darius I sent the Greek explorer Scylax of Caryanda to sail down the Indus River, heading a team of spies, in order to explore the course of the Indus River. After a periplus of 30 months, Scylax is said to have returned to Egypt near the Red Sea, and the seas between the Near East and India were made use of by Darius.

Herodotus names the territories of Gandāra, Sattagydia, Dadicae and Aparytae as the 7th province of the Achaemenid Empire for tax-payment purposes, while Indus (called Ἰνδός, "Indos" in Greek sources) formed the 20th tax region.

Achaemenid army during the invasion

Throughout its existence, the Achaemenids were constantly engaging in wars, either through conquering new territories or by quelling rebellions throughout the empire. To fulfil this need, the Achaemenid Empire had to maintain a professional standing army which levied and employed personnel from all of its satraps and territories.

The Achaemenid army was not uniquely Persian. Rather it was composed of many different ethnicities that were part of the vast and diverse empire. Herodotus gives a full list of the ethnicities of the Achaemenid army, in which are included Bactrians, Sakas (Scythians), Parthians, Sogdians, Ionians (Greeks), Egyptians, Ethiopians, etc.Herodotus VII 65 These ethnicities are likely to have been included in the Achaemenid army during the invasions of India.

Achaemenid royal inscriptions

These events were recorded in the Achaemenid royal inscriptions such as the Behistun inscription and the Naqsh-e Rostam inscription, as well as the accounts of Herodotus (483–431 BCE). 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. Hecataeus of Miletus (circa 500 BCE) also wrote about the "Indus Satrapies" of the Achaemenids.

Behistun inscription The 'DB' Behistun inscription of Darius I (circa 510 BCE) mentions Gandāra (𐎥𐎭𐎠𐎼, Gadāra) and the adjacent territory of Sattagydia (𐎰𐎫𐎦𐎢𐏁, Thataguš) as part of the Achaemenid Empire:

From the dating of the Behistun inscription, it is possible to infer that the Achaemenids first conquered the areas of Gandāra and Sattagydia circa 518 BCE.

Statue of Darius inscriptions Hinduš is also mentioned as one of 24 subject countries of the Achaemenid Empire, illustrated with the drawing of a kneeling subject and a hieroglyphic cartridge reading 𓉔𓈖𓂧𓍯𓇌 (h-n-d-wꜣ-y), on the Egyptian statue of Darius I, now in the National Museum of Iran. Sattagydia also appears (𓐠𓂧𓎼𓍯𓍒, sꜣ-d-g-wꜣ-ḏꜣ, Sattagydia), and probably Gandāra (𓉔𓃭𓐍𓂧𓇌, h-rw-ḫ-d-y, although this could be Arachosia), with their own illustrations.

Apadana Palace foundation tablets

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. This is known as the DPh inscription. The deposition of these foundation tablets and the Apadana coin hoard found under them, is dated to circa 515 BCE.

Naqsh-e Rustam inscription

The DSe inscription and DSm inscriptionDSm inscription of Darius in Susa gives Thataguš (Sattagydia), Gadāra (Gandāra) and Hiduš (Hindush) among the nations that he rules.

Hidūš (𐏃𐎡𐎯𐎢𐏁 in Old Persian cuneiform) also appears later as a satrapy in the Naqsh-i-Rustam inscription at the end of the reign of Darius, who died in 486 BCE. The DNa inscription on Darius' tomb at Naqsh-i-Rustam near Persepolis records Gadāra (Gandāra) along with Hiduš and Thataguš (Sattagydia) in the list of satrapies.

Achaemenid administration

The nature of the administration under the Achaemenids is uncertain. Even though the Indian provinces are called "satrapies" by convention, there is no evidence of there being any satraps in these provinces. When Alexander invaded the region, he did not encounter Achaemenid satraps in the Indian provinces, but local Indian rulers referred to as hyparchs ("Vice-Regents"), a term that connotes subordination to the Achaemenid rulers. The local rulers may have reported to the satraps of Bactria and Arachosia.

Achaemenid lists of provinces Darius I listed three Indian provinces: Sattagydia (Thataguš), Gandāra (Gandhara) and Hindush (Hidūš), in which Hidūš should be understood as Indus Valley, in the Naqsh-e Rustam inscription.

Gandāra included the entire Peshawar Valley which was bound by the Swat Valley in the north, Bactria in the west, the Indus River to the south-east, and Sattagydia in the south. The capital of the Gandāra satrapy was Puṣkalāvatī. Archeological excavations of Puṣkalāvatī were conducted by Mortimer Wheeler in 1962 who discovered structures built during the Achaemenid period as well as artifacts.The Achaemenid satrapy of Hindush incorporated the greater Punjab region in the Indus Valley. It was bound by the Hazara region to the north, the Indus River to the west, and the Jhelum River in the south and east. The capital was probably Bhir Mound in Taxila. Bhir Mound was excavated by John Marshall between 1913 and 1934. Fortified structures and canals were found dating to the Achaemenid period, as well as ornamental jewelry.