Achaemenid conquest of the Indus Valley
Around 535 BCE, the Persian king Cyrus the Great initiated a protracted campaign to absorb parts of northwestern Indian subcontinent 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.
Source: Wikipedia — Achaemenid conquest of the Indus Valley (CC BY-SA 4.0)