Accordingly, Seleucus ceded to Chandragupta his northwestern territories, possibly as far as Arachosia and received 500 war elephants (which played a key role in the victory of Seleucus at the Battle of Ipsus): The Indians occupy in part some of the countries situated along the Indus, which formerly belonged to the Persians: Alexander deprived the Ariani of them, and established there settlements of his own.But Seleucus Nicator gave them to Sandrocottus in consequence of a marriage contract, and received in return five hundred elephants.
In 326 BC, Alexander the Great conquered the northwestern part of the Indian subcontinent as far as the Hyphasis River, and established satrapies and founded several settlements, including Bucephala; he turned south when his troops refused to go further east.
The Indian satrapies of the Punjab were left to the rule of Porus and Taxiles, who were confirmed again at the Treaty of Triparadisus in 321 BC, and remaining Greek troops in these satrapies were left under the command of general Eudemus.
The Greeks in the Indian Subcontinent were eventually divided from the Graeco-Bactrians centered in Bactria (now the border between Afghanistan and Uzbekistan), and the Indo-Greeks in the present-day north-western Indian Subcontinent.
The most famous Indo-Greek ruler was Menander (Milinda).
His son, Demetrius I, founder of the Indo-Greek kingdom, was therefore of Greek ethnicity at least by his father.
A marriage treaty was arranged for the same Demetrius with a daughter of the Seleucid ruler Antiochus III (who had some Persian descent).
He had his capital at Sakala in the Punjab (present-day Sialkot).
The expression "Indo-Greek Kingdom" loosely describes a number of various dynastic polities, traditionally associated with a number of regional capitals like Taxila, Other potential centers are only hinted at; for instance, Ptolemy's Geographia and the nomenclature of later kings suggest that a certain Theophila in the south of the Indo-Greek sphere of influence may also have been a satrapal or royal seat at one time.
During the two centuries of their rule, the Indo-Greek kings combined the Greek and Indian languages and symbols, as seen on their coins, and blended Greek and Indian ideas, as seen in the archaeological remains.