Megasthenes is known as a Greek ambassador or envoy connected with Seleucus I and Chandragupta Maurya. He spent time in India and at the Mauryan court, but the exact chronology of his embassy and its relationship to the Seleucid-Mauryan settlement are not known with enough precision to make him securely part of one dated diplomatic exchange. His experiences nevertheless gave him access to a political world that most Greek writers knew only at second hand.

The Indica itself is lost and survives through quotations and summaries in later writers such as Strabo, Arrian, Diodorus and Pliny. Later testimony is often used to reconstruct the work as four books, but the original structure cannot now be checked against a surviving manuscript. Modern editions number and arrange the fragments differently, so a fixed total such as forty-three should be understood as an editorial system rather than the ancient book's own surviving numbering.

Megasthenes described India as a vast country defined by major rivers, mountains, monsoon conditions and the southern ocean. He gave measurements in stades and discussed both the Indus and Ganges systems. Taprobane in later Greco-Roman geography is generally identified with Sri Lanka, although ancient authors varied greatly in their measurements and descriptions of the island. The Indica helped move Greek geographical interest well beyond the Indus frontier familiar from earlier writers.

The Indus and Ganges dominate the fragments. Megasthenes described the Indus system and its tributaries, the peoples of the Punjab, the roads from Taxila and the eastern plains watered by the Ganges. His measurements were sometimes fantastic. Strabo objected that no one could accurately measure such enormous distances and that Megasthenes exaggerated the size of Taprobane and the eastern ocean. Yet the fragments preserve genuine river geography and an early awareness that the Ganges was the centre of a great eastern kingdom.

Megasthenes' description of Pataliputra is among the most important surviving fragments. He reports a very large city enclosed by timber defences, with hundreds of towers and dozens of gates. Archaeology at ancient Pataliputra has confirmed major wooden construction, including palisade remains and monumental architecture, which makes the general picture of a timber-built Mauryan capital plausible. The archaeological evidence does not independently verify every ancient number of gates, towers or dimensions.

The Indica described Chandragupta's state as a military and administrative machine. It reported enormous armies of infantry, cavalry, elephants and chariots, with elephants serving as instruments of royal power. Greek readers marvelled at the war elephants that Alexander's companions had already encountered under Porus. Megasthenes also described the royal road, the officers who supervised agriculture, irrigation, commerce and justice, and the systematic control that allowed a single ruler to govern the Ganges plain. Some of these details may preserve Mauryan administration; others reflect Greek expectations about oriental monarchy.

Megasthenes famously divided Indian society into seven hereditary occupational or social groups. Later writers often call these 'castes', but his sevenfold scheme does not correspond directly to the four-varna model known from Brahmanical sources. It is therefore safer to describe the passage as Megasthenes' Greek classification of Indian society rather than a literal transcription of one indigenous caste system.

Greek writers using Megasthenes distinguish several kinds of Indian philosophers and ascetics, including Brahmans and groups rendered with terms such as Sarmanes or Gymnosophists. These labels do not map neatly onto one modern religious category. The fragments remain valuable evidence for Greek encounters with Indian intellectual and ascetic traditions, but their terminology is filtered through Greek ethnographic habits.

The Indica gave Greek readers their first systematic account of Indian religion. Megasthenes discussed Brahmin theories of the cosmos, their ideas about generation, their rituals, their clothing and their customs of property. He reported Indian practices concerning the disposal of the dead, the honouring of ancestors and the teaching of sacred knowledge. Some passages preserve accurate Indian material; others project Greek philosophy onto Indian teachers. Dahlquist and other scholars have treated the fragments as evidence of early contact between Greek philosophical categories and Brahmanical thought.

Nature receives as much attention as politics. Megasthenes described the monsoon, the cotton plant, the banyan tree, the pepper vine, the trees that yielded fragrant products and the animals of the forests. He mentions elephants, tigers, enormous snakes, one-horned animals, Indian dogs and strange creatures unknown to Greece. Many of these reports have historical foundations distorted by distance. The one-horned animal may be the rhinoceros; the giant ants that dug gold may be Himalayan marmots or miners; the winged serpents may combine real accounts of large snakes with Near Eastern imagery. The Indica therefore preserves the first stage in a long process by which Indian nature entered Greek paradoxography.

Gold-digging ants became one of the most famous marvels attached to India in Greek literature. Herodotus already tells a related story, and later reports keep the motif alive. Modern attempts to explain the tale through Himalayan marmots, mining practices or misunderstood local reports are hypotheses, not an established identification of what Megasthenes or earlier writers actually meant.

His work also contained mythology. Megasthenes reported Indian traditions of Heracles and Dionysus as ancient visitors to India. Greeks had already interpreted foreign gods through their own pantheon; Herodotus used the same method for Egyptian religion. In the Indica, Heracles becomes an ancient Indian hero, and Dionysus leaves wine, ivy and ritual memory in the mountains. These passages are not proof that Indians worshipped Greek gods. They show how Greeks made a foreign world intelligible by attaching familiar divine names to local traditions.

Arrian praised Megasthenes for his serious treatment of India and used him extensively in the Indica, while admitting that earlier writers disagreed. Strabo preserved more fragments than any other author but attacked the work's measurements and wonders. Pliny used Megasthenes for Indian geography, luxury goods and natural history. Diodorus compressed his account into books two and five. Athenaeus quoted him for animals, food and court customs. Through these authors the lost original became a quarry for every later account of India.

The work must be read beside Indian evidence. The Arthashastra, Brahmanical texts, Buddhist sources and the inscriptions of Ashoka reveal the administrative, religious and political world of the Mauryan Empire. Archaeology at Pataliputra, Taxila and other sites tests the Greek descriptions. Megasthenes remains indispensable because he wrote before Ashoka and because his work is the longest outsider's account of Chandragupta's kingdom. He is not a substitute for Indian sources, but he preserves a perspective Indian texts do not provide.

The Indica is also a political text. Megasthenes wrote after a treaty that recognised Chandragupta's power and gave Seleucus elephants and diplomatic prestige. His descriptions of the Indian king's army, court and roads served Greek imperial knowledge. India was both the eastern limit of Alexander's conquests and a partner in the Seleucid world. The work therefore joins ethnography to diplomacy: it explains the empire with which the Greeks must now negotiate.

Its reliability varies by subject. Rivers, roads, cities, castes, monsoon agriculture, elephants, cotton and ascetic groups have plausible historical foundations. Precise army numbers, the dimensions of Taprobane, giant ants and many animals belong to the ancient taste for wonder. Even the errors reveal Greek expectations. A rich eastern empire needed to be measured; a strange land needed monsters; a philosophical people needed Brahmins who could be compared with Greek sages.

Later geography depended on the Indica. Eratosthenes used it to place India within the measured oikoumene. Hipparchus corrected its distances. Strabo criticised and preserved it. Ptolemy used later trade reports but inherited the Megasthenic frame of rivers, south-pointing coast and Taprobane. Roman authors quoted it when describing pearls, diamonds, cotton and pepper. Through Arrian, the Indica survived as one of the principal ancient accounts of India.

Modern scholarship has reconstructed the fragments through the editions of Jacoby, Schwanbeck, McCrindle, and most recently Duane Roller's Brill's New Jacoby commentary. The result is not a recovered book but a mosaic. Historians compare each fragment with its quoting author, ask what the compiler may have changed and weigh Greek categories against Indian evidence. The Indica is valuable precisely because it survives in pieces: every fragment carries the trace of a later reader who found India worth remembering.

The Indica should not be confused with Ctesias' earlier Indica, which was full of marvels and unreliable reports, or with Arrian's later Indica, which synthesised Nearchus, Megasthenes and other sources during the Roman Empire. Ctesias wrote before Alexander from Persian court knowledge; Arrian wrote after centuries of contact; Megasthenes stands between them as the only extensive Greek account based on direct residence in a Mauryan court.