The sources which are used to reconstruct the history of the Indo-Greeks are few and disparate, leading to much uncertainty about the precise state of the Indo-Greek kingdom and its chronology. Sources related to the Indo-Greeks can be classified into various categories: ancient literary sources from both the West and the Indian world, archaeological sources from the general area of present day Pakistan, Kashmir and North Indian states of Punjab, Haryana, Himachal Pradesh, Uttar Pradesh & Bihar, and numismatical sources, which are abundant and well-preserved but often rather cryptic.

Literary sources

Western literary sources Some narrative history has survived for most of the Hellenistic world, at least of the kings and the wars;See Polybius, Arrian, Livy, Cassius Dio, and Diodorus. Justin, who will be discussed shortly, provides a summary of the histories of Hellenistic Macedonia, Egypt, Asia, and Parthia. this is lacking for India. The main Greco-Roman source on the Indo-Greeks is Justin, who wrote an anthology drawn from the Roman historian Pompeius Trogus, who in turn wrote, from Greek sources, at the time of Augustus Caesar.For the date of Trogus, see the OCD on "Trogus" and Yardley/Develin, p. 2; since Trogus' father was in charge of Julius Caesar's diplomatic missions before the history was written (Justin 43.5.11), Senior's date in the following quotation is a terminus post quem: "The Western sources for accounts of Bactrian and Indo-Greek history are: Polybius, a Greek born c.200 BC; Strabo, a Roman who drew on the lost history of Apollodoros of Artemita (c.130-87 BC), and Justin, who drew on Trogus, a post 87 BC writer", Senior, Indo-Scythian coins IV, p.x; the extent to which Strabo is citing Apollodorus is disputed, beyond the three places he names Apollodorus (and he may have those through Eratosthenes). Polybius speaks of Bactria, not of India. Justin tells the parts of Trogus' history he finds particularly interesting at some length; he connects them by short and simplified summaries of the rest of the material. In the process he has left 85% to 90% of Trogus out; and his summaries are held together by phrases like "meanwhile" (eodem tempore) and "thereafter" (deinde), which he uses very loosely. Where Justin covers periods for which there are other and better sources, he has occasionally made provable mistakes. As Tarn and Develin both point out, Justin is not trying to write history in our sense of the word; he is collecting instructive moral anecdotes.Justin, Epitome of the Philippic History of Pompeius Trogus translated by J. C. Yardley, notes and introduction by Robert Develin. (Atlanta 1994). The source for these paragraphs, and the next insofar as it is not Justin, is the Introduction pp. 1-11. See also Tarn (1951) p.50. Justin does find the customs and growth of the Parthians, which were covered in Trogus' 41st book, quite interesting, and discusses them at length; in the process, he mentions four of the kings of Bactria and one Greek king of India, getting the names of two of them wrong.Justin, 41.4.5, 41.4.8-9, 41.6.1-5, ed. cit.; Diodotus I and II, whom Justin calls Theodotus; Eucratides and his unnamed parricidal son; and "Demetrius, king of the Indians" (so Yardley: Indorum rex, Develin's note implies this is Demetrius II, but suggests that Demetrius I and II may be the same person.) Theodotus, while unquestionably Justin's text, is an error; no coins support his existence, and Trogus' tables of contents (the so-called prologues) survive (Develin and Yardley, p.284) saying Diodotus; they also include Indicae quoque res additae, gestae per Apollodotum et Menandrum, reges eorum "some Indian matters, namely the achievements of the Indian kings, Apollodotus and Menander.", although Justin does not mention Apollodotus. Tarn, Narain, and Bopearchchi all correct to Diodotus.

In addition to these dozen sentences, the geographer Strabo mentions India a few times in the course of his long dispute with Eratosthenes about the shape of Eurasia. Most of these are purely geographical claims, but he does mention that Eratosthenes' sources say that some of the Greek kings conquered further than Alexander; Strabo does not believe them on this, but modern historians do; nor does he believe that Menander and Demetrius son of Euthydemus conquered more tribes than AlexanderStrabo, Geographia 11.11.1 p.516 Casaubon. 15.1.2, p. 686 Casaubon, "tribes" is Jones' version of ethne (Loeb) There is half a story about Bactria (only) in one of the books of Polybius which has not come down to us intact.For a list of classical testimonia, see Tarn's Index II; but this covers India, Bactria, and several sources for the Hellenistic East as a whole.

In the 1st century BCE, the geographer Isidorus of Charax mentions Parthians ruling over Greek populations and cities in Arachosia: "Beyond is Arachosia. And the Parthians call this White India; there are the city of Biyt and the city of Pharsana and the city of Chorochoad and the city of Demetrias; then Alexandropolis, the metropolis of Arachosia; it is Greek, and by it flows the river Arachotus. As far as this place the land is under the rule of the Parthians.""Parthians stations", 1st century BCE. Mentioned in Bopearachchi, "Monnaies Greco-Bactriennes et Indo-Grecques", p52. Original text in paragraph 19 of Parthian stations

According to Strabo, Greek advances temporarily went as far as the Shunga capital Pataliputra (today Patna) in eastern India:

The 1st century BCE Greek historian Apollodorus, quoted by Strabo, affirms that the Bactrian Greeks, led by Demetrius I and Menander, conquered India and occupied a larger territory than the Macedonian Greeks under Alexander the Great, going beyond the Hypanis towards the Himalayas:Strabo quoting Apollodorus on the extent of Greek conquests: "Apollodorus, for instance, author of the Parthian History, when he mentions the Greeks who occasioned the revolt of Bactriana from the Syrian kings, who were the successors of Seleucus Nicator, says, that when they became powerful they invaded India. He adds no discoveries to what was previously known, and even asserts, in contradiction to others, that the Bactrians had subjected to their dominion a larger portion of India than the Macedonians; for Eucratides (one of these kings) had a thousand cities subject to his authority." Strabo 15-1-3 Full text "The Greeks who caused Bactria to revolt grew so powerful on account of the fertility of the country that they became masters, not only of Ariana, but also of India, as Apollodorus of Artemita says: and more tribes were subdued by them than by Alexander — by Menander in particular (at least if he actually crossed the Hypanis towards the east and advanced as far as the Imaüs), for some were subdued by him personally and others by Demetrius, the son of Euthydemus the king of the Bactrians." (Strabo 11.11.1 Full text)

The Roman historian Justin also mentioned the Indo-Greek conquests, describing Demetrius as "King of the Indians" ("Regis Indorum"), and explaining that after vanquishing him Eucratides in turn "put India under his rule" ("Indiam in potestatem redegit")Justin on Demetrius "King of the Indians": "Multa tamen Eucratides bella magna uirtute gessit, quibus adtritus cum obsidionem Demetrii, regis Indorum, pateretur, cum CCC militibus LX milia hostium adsiduis eruptionibus uicit. Quinto itaque mense liberatus Indiam in potestatem redegit." ("Eucratides led many wars with great courage, and, while weakened by them, was put under siege by Demetrius, king of the Indians. He made numerous sorties, and managed to vanquish 60,000 enemies with 300 soldiers, and thus liberated after four months, he put India under his rule") (since the time of the embassies of Megasthenes in the 3rd century BCE "India" was understood as the entire subcontinent, and was cartographed by geographers such as Eratosthenes). Justin also mentions Apollodotus and Menander as kings of the Indians."Indicae quoque res additae, gestae per Apollodotum et Menandrum, reges eorum": "Also included are the exploits in India by Apollodotus and Menander, their kings" Justin, quoted in E.Seldeslachts, p284

Greek and Indian sources tend to indicate that the Greeks campaigned as far as Pataliputra until they were forced to retreat following the coup staged by Eucratides back in Bactria circa 170 BCE, suggesting an occupation period of about eight years."Pataliputra fut occupée par les forces coalisées Grecques pendant presque huit ans" ("Pataliputra was occupied by the Greek coalition for about eight years"), Mario Bussagli, "L'Art du Gandhara", p100 Alternatively, Menander may merely have joined a raid led by Indian Kings down the Ganges (A.K. Narain and Keay 2000), as Indo-Greek territory has only been confirmed from the Kabul Valley to the Punjab.

To the south, the Greeks occupied the areas of the Sindh and Gujarat down to the region of Surat (Greek: Saraostus) near Mumbai (Bombay), including the strategic harbour of Barygaza (Bharuch),"Menander became the ruler of a kingdom extending along the coast of western India, including the whole of Saurashtra and the harbour Barukaccha. His territory also included Mathura, the Punjab, Gandhara and the Kabul Valley", Bussagli p101) as attested by several writers (Strabo 11; Periplus of the Erythraean Sea, Chap. 41/47) and as evidenced by coins dating from the Indo-Greek ruler Apollodotus I:

The 1st century CE Periplus of the Erythraean Sea describes numerous Greek buildings and fortifications in Barigaza, although mistakenly attributing them to Alexander, and testifies to the circulation of Indo-Greek coinage in the region:

From ancient authors (Pliny, Arrian, Ptolemy and Strabo), a list of provinces, satrapies, or simple regional designations, and Greek cities from within the Indo-Greek Kingdom can be discerned (though others have been lost), ranging from the Indus basin to the upper valley of the Ganges.Greek provinces in India according to Classical sources: Patalene - the whole Indus delta region, with an apparent capital in "Demetrias-in-Patalene;" presumably founded by Demetrius (Ptolemy, Geographia, VII 1, 55/ Strabo 11.11.1) Abiria - North of the Indus delta and apparently named for the Ahbira peoples, presumably in residence of the region. (Ptolemy, Geographia, VII 1, 55). Prasiane - North of Abiria and East of the main Indus channel. (Pliny, Natural history, VI 71) Surastrene - Southeast of Patalene, comprising the Kathiawar peninsula and parts of Gujarat to Bharuch (modern Saurashtra and Surat), with the city of "Theophila". (Ptolemy, Geographia, VII 1, 55/ Strabo 11.11.1/ Periplus, Chap.41–47). Sigerdis - a coastal region beyond Patalene and Surastrene, thought to correspond to Sindh. (Strabo 11.11.1) Souastene - subdivision of Gandhara, comprising the Swat Valley (Ptolemy, Geographia, VII 1, 42). Goryaea - smaller district located between the lower Swat river and the Kunar (Bajaur), with the city of "Nagara, also called Dionysopolis". (Ptolemy, Geographia, VII 1, 42). Peucelaitas - denotes the immediate district around Pushkalavati (Greek: Peucela). (Arrian, On India, IV 11) Kaspeiria - comprising the upper valleys of the Chenab, Ravi, and Jhelum (ie, southern Kashmir). (Ptolemy, Geographia, VII 1, 42). Pandouorum - Region of the Punjab along the Hydaspes river, with the "city of Sagala, also called Euthydemia" and another city named "Bucephala" (Ptolemy, Geographia, VII 1), or "Bucephalus Alexandria" (Periplus, 47). Kulindrene - as related by Ptolemy, a region comprising the upper valleys of the Sutlej, Jumna, Beas, and Ganges. This report may be inaccurate, and the contents of the region somewhat smaller. (Ptolemy, Geographia, VII 1, 42).

Indian literary sources