Pantaleon, who reigns in Arachosia, some time between 190 BCE and 180 BCE, is one of the most enigmatic of the Greek kings in Bactria and India.

A younger contemporary or successor of the Greco-Bactrian king Demetrius, he is sometimes believed to have been his brother and/or subking.

He is the first Greek king to strike Indian coins, peculiar irregular bronzes which suggests he has his base in Arachosia and Gandhara and wants support from the native population.

The limited size of his coinage indicates a short reign.

Known evidence suggests that he is replaced by his (probable) brother or son Agathocles, by whom he is commemorated on a "pedigree" coin.

Some of his coins (as well as those of Agathocles and Euthydemus II) have another surprising characteristic: these kings are the first in the world to issue coins of copper-nickel (75/25 ratio) alloy, a technology that will not be developed in the West until the eighteenth century, but is known by the Chinese at this time, as some weapons from China’s Warring States Period are known to have been made from the copper-nickel alloy known as "white copper".

This suggests that exchanges of the metallic alloy, or possibly exchanges of technicians, are occurring at this time between China and the region of Bactria.

The practice of exporting Chinese metals, in particular iron, for trade is attested around this period.

Taxila, or Takshashila, in the western Punjab (today represented by the remains in the present Bhir Mound) had become a great Buddhist center of learning during the reign of Ashoka, grandson of Chandragupta Maurya, founder of the Mauryan empire in eastern India.

Nonetheless, Taxila had briefly been the center of a minor local rebellion, subdued only a few years after its onset.

Two years after the assassination of the last Maurya emperor in 185, the Greco-Bactrian King Demetrius, who had succeeded his father Euthydemus around 200 BCE and conquered extensive areas in what now is eastern Iran and Afghanistan, led his troops across the Hindu Kush to conquer Gandhāra, the Punjab and the Indus valley, thus creating an Indo-Greek kingdom far from Hellenistic Greece.

It is generally considered that Demetrius ruled in Taxila (where many of his coins will be found in the archaeological site of Sirkap, on the opposite bank of the Tamranal River from Taxila.

The Indian records also describe Greek attacks on Saketa, Panchala, Mathura and Pataliputra.)

Demetrius I dies of unknown reasons, and the date 180 BCE is merely a suggestion aimed to allow suitable regnal periods for subsequent kings, of which there are to be several.

Even if some of them are co-regents, civil wars and temporary divisions of the empire are most likely.

The kings Pantaleon, Antimachus, Agathocles and possibly Euthydemus II rule after Demetrius I, and theories about their origin include all of them being relatives of Demetrius I, or only Antimachus.

Eventually, the kingdom of Bactria would fall to the able newcomer Eucratides, who in about 171 would uproot the Euthydemid dynasty of Greco-Bactrian kings and replace it with his own lineage.

Buddhism flourishes in the realms of the Bactrian kings.

The Sunga Empire's wars with the Indo-Greek Kingdom figure greatly in the history of this age, although the net result of these wars remains uncertain.