Page "Seleucus I Nicator" Paragraph 48

Always lying in wait for the neighboring nations, strong in arms and persuasive in council, he acquired Mesopotamia, Armenia, ' Seleucid ' Cappadocia, Persis, Parthia, Bactria, Arabia, Tapouria, Sogdia, Arachosia, Hyrcania, and other adjacent peoples that had been subdued by Alexander, as far as the river Indus, so that the boundaries of his empire were the most extensive in Asia after that of Alexander.

The whole region from Phrygia to the Indus was subject to Seleucus.

He crossed the Indus and waged war with Sandrocottus, king of the Indians, who dwelt on the banks of that stream, until Seleucus lost the war and they came to an understanding with each other and contracted a marriage relationship.

– Appian, History of Rome, The Syrian Wars 55