Seleucus soon turned his attention once again eastward.
In the year 305 BC, Seleucus I Nicator went to India and apparently occupied territory as far as the Indus, and eventually waged war with the Maurya Emperor Chandragupta Maurya.

	
Only a few sources mention his activities in India.
Chandragupta (known in Greek sources as Sandrokottos), founder of the Mauryan empire, had conquered the Indus valley and several other parts of the easternmost regions of Alexander's empire.
Seleucus began a campaign against Chandragupta and crossed the Indus.
Seleucus' Indian campaign was, however, a failure.
It is unknown what exactly happened.
Perhaps Chandragupta defeated Seleucus in battle.
No sources mention this, however.
But as most western historians note, Seleucus appears to have fared poorly as he did not achieve his aims.
The two leaders ultimately reached an agreement, and through a treaty sealed in 305 BC, Seleucus ceded a considerable amount of territory to Chandragupta in exchange for 500 war elephants, which were to play a key role in the forthcoming battles, particularly at Ipsus.
The Maurya king might have married the daughter of his Greek rival.
According to Strabo, the ceded territories bordered the Indus:
The geographical position of the tribes is as follows: along the Indus are the Paropamisadae, above whom lies the Paropamisus mountain: then, towards the south, the Arachoti: then next, towards the south, the Gedroseni, with the other tribes that occupy the seaboard; and the Indus lies, latitudinally, alongside all these places; and of these places, in part, some that lie along the Indus are held by Indians, although they formerly belonged to the Persians.
Alexander [III 'the Great' of Macedon] took these away from the Arians and established settlements of his own, but Seleucus Nicator gave them to Sandrocottus [Chandragupta], upon terms of intermarriage and of receiving in exchange five hundred elephants. —
Strabo 15.2.9
From this, it seems that Seleucus surrendered the easternmost provinces of Arachosia, Gedrosia, Paropamisadae and perhaps also Aria.
On the other hand, he was accepted  by other satraps of the eastern provinces.
His Iranian wife, Apama, may have helped him implement his rule in Bactria and Sogdiana .
This would tend to be corroborated archaeologically, as concrete indications of Mauryan influence, such as the inscriptions of the Edicts of Ashoka which are known to be located in, for example, Kandhahar in today's southern Afghanistan.

Some authors claim that the argument relating to Seleucus handing over more of what is now southern Afghanistan is an exaggeration originating in a statement by Pliny the Elder referring not specifically to the lands received by Chandragupta, but rather to the various opinions of geographers regarding the definition of the word "India":
Most geographers, in fact, do not look upon India as bounded by the river Indus, but add to it the four satrapies of the Gedrose, the Arachotë, the Aria, and the Paropamisadë, the River Cophes thus forming the extreme boundary of India.
According to other writers, however, all these territories, are reckoned as belonging to the country of the Aria.
 — Pliny, Natural History VI, 23
Also the passage of Arrian explaining that Megasthenes lived in Arachosia with the satrap Sibyrtius, from where he travelled to India to visit Chandragupta Maurya, goes against the notion that Arachosia was under Maurya rule:
Megasthenes lived with Sibyrtius, satrap of Arachosia, and speaks of his often visiting Sandracottus, the king of the Indians.
 — Arrian, Anabasis Alexandri v,6
Nevertheless, it is usually considered today that Arachosia and the other three regions did become dominions of the Mauryan Empire.

The alliance between Chandragupta and Seleucus was affirmed with a marriage (Epigamia).
Chandragupta or his son may have married a daughter of Seleucus, or perhaps there was diplomatic recognition of intermarriage between Indians and Greeks.
An Indian Puranic source, the Pratisarga Parva of the Bhavishya Purana, also described the marriage of Chandrag
Seleucus soon turned his attention once again eastward. In the year 305 BC, Seleucus I Nicator went to India and apparently occupied territory as far as the Indus, and eventually waged war with the Maurya Emperor Chandragupta Maurya.
	
Only a few sources mention his activities in India. Chandragupta (known in Greek sources as Sandrokottos), founder of the Mauryan empire, had conquered the Indus valley and several other parts of the easternmost regions of Alexander's empire. Seleucus began a campaign against Chandragupta and crossed the Indus. Seleucus' Indian campaign was, however, a failure. It is unknown what exactly happened. Perhaps Chandragupta defeated Seleucus in battle. No sources mention this, however. But as most western historians note, Seleucus appears to have fared poorly as he did not achieve his aims. The two leaders ultimately reached an agreement, and through a treaty sealed in 305 BC, Seleucus ceded a considerable amount of territory to Chandragupta in exchange for 500 war elephants, which were to play a key role in the forthcoming battles, particularly at Ipsus. The Maurya king might have married the daughter of his Greek rival. According to Strabo, the ceded territories bordered the Indus:
The geographical position of the tribes is as follows: along the Indus are the Paropamisadae, above whom lies the Paropamisus mountain: then, towards the south, the Arachoti: then next, towards the south, the Gedroseni, with the other tribes that occupy the seaboard; and the Indus lies, latitudinally, alongside all these places; and of these places, in part, some that lie along the Indus are held by Indians, although they formerly belonged to the Persians. Alexander [III 'the Great' of Macedon] took these away from the Arians and established settlements of his own, but Seleucus Nicator gave them to Sandrocottus [Chandragupta], upon terms of intermarriage and of receiving in exchange five hundred elephants. — Strabo 15.2.9
From this, it seems that Seleucus surrendered the easternmost provinces of Arachosia, Gedrosia, Paropamisadae and perhaps also Aria. On the other hand, he was accepted  by other satraps of the eastern provinces. His Iranian wife, Apama, may have helped him implement his rule in Bactria and Sogdiana . This would tend to be corroborated archaeologically, as concrete indications of Mauryan influence, such as the inscriptions of the Edicts of Ashoka which are known to be located in, for example, Kandhahar in today's southern Afghanistan.
Some authors claim that the argument relating to Seleucus handing over more of what is now southern Afghanistan is an exaggeration originating in a statement by Pliny the Elder referring not specifically to the lands received by Chandragupta, but rather to the various opinions of geographers regarding the definition of the word "India":
Most geographers, in fact, do not look upon India as bounded by the river Indus, but add to it the four satrapies of the Gedrose, the Arachotë, the Aria, and the Paropamisadë, the River Cophes thus forming the extreme boundary of India. According to other writers, however, all these territories, are reckoned as belonging to the country of the Aria.  — Pliny, Natural History VI, 23
Also the passage of Arrian explaining that Megasthenes lived in Arachosia with the satrap Sibyrtius, from where he travelled to India to visit Chandragupta Maurya, goes against the notion that Arachosia was under Maurya rule:
Megasthenes lived with Sibyrtius, satrap of Arachosia, and speaks of his often visiting Sandracottus, the king of the Indians.  — Arrian, Anabasis Alexandri v,6
Nevertheless, it is usually considered today that Arachosia and the other three regions did become dominions of the Mauryan Empire.
The alliance between Chandragupta and Seleucus was affirmed with a marriage (Epigamia). Chandragupta or his son may have married a daughter of Seleucus, or perhaps there was diplomatic recognition of intermarriage between Indians and Greeks. An Indian Puranic source, the Pratisarga Parva of the Bhavishya Purana, also described the marriage of Chandrag
Seleucus I Nicator