Extent of conquests made in India by Cyrus: The founder of the Achaemenid Empire in Persia, Cyrus, led some campaigns to the east of Iran between 558 and 530 B.C. In course of these campaigns he probably invaded the Indian borderland. According to some historians, some Indian king sent an embassy to Cyrus to pay him tribute. On this basis, it is supposed that Cyrus had conquered the borderland between India and Iran and received tributes from some Indian king.
The Indian conquests of Darius: In the reign of Darius I (522-486 B.C.) the Persians made some real advance in India. The Bahistan Inscription mentions Gandhara as a province of his empire which Darius might have inherited from Cyrus. This is further confirmed by the Susa Palace Inscription of Darius which mentions that teak was brought from Gandhara for the construction of the palace of the Emperor. Gandhara means modern Peshawarand Rawalpindi of Pakistan.
The statement of Herodotus: According to him, India formed the twentieth satrapy of the empire of Darius paying a tribute of 360 talents of gold dust. This gold was probably collected from the beds of the upper Indus and from the gold mines of Dardistan. Herodotus has also recorded that Darius sent a naval expedition probably in 517 B.C. to explore the Indus basin.
The extent of Darius Empire in India: The extent of the Persian Empire in India under Darius was not merely confined to Gandhara alone but extended further towards the Indus as well. The Persian Empire in India reached its farthest limit under Darius. The extent of the Indian dominion of Darius included the territories inherited from his predecessors and those he conquered in India. They territories of West Punjab and Lower Indus valley were under Persian rulers . That the Persian Empire under Darius did not extend beyond this limit is inferred from the silence of Herodotus about the Magadha Empire in the Ganges valley.
Persian domination over India under Xerxes and his successors: Xerxes, the successor of Darius I kept his flag flying over the Indian kingdom which he had inherited from Darius, but he failed to make any forward movement in India due to his commitments in over India under Greece. Herodotus states that Xerxes requisitioned large number of troops including infantry and cavalry from India for invasion of Greece.
The downfall of Persian Empire: The defeat suffered by Xerxes in Greece led to decline of Persian power in India. However, the Achaemenid rule over India continued up to 330 B.C. In that year Darius III, the last of the Achaemenid ruler summoned Indian troops to fight against Alexander the Great. With the fall of the Persian power under the impact of the invasion of Alexander the Great, the Persian hold over India was lost.