Megasthenes
Megasthenes (ca. 350 BC - 290 BC) was a Greek traveller and geographer. He was born in Asia Minor and became an ambassador of Seleucus I of Syria to the court of Sandrocottus (Chandragupta Maurya) of India, in Pataliputra. However the exact date of his embassy is uncertain. Scholars place it before 288 BC, which was the date of Chandragupta's death.
Arrian explains that Megasthenes lived in Arachosia, with the satrap Sibyrtius, from where he visited India:
"Megasthenes lived with Sibyrtius, satrap of Arachosia, and often speaks of his visiting Sandracottus, the king of the Indians." Arrian, Anabasis Alexandri [1]
We have more definite information regarding the parts of India which Megasthenes visited. He entered the country through the district of the Pentapotamia of the rivers of which he gave a full account (thought to be the five affluents of the Indus, forming the Punjab region), and proceeded from there by the royal road to Pataliputra. There are accounts of Megasthenes having visited Madurai (then, a bustling city and capital of Pandya Kingdom), but appears not to have visited any other parts of India. His observations were recorded in Indika, a work that served as an important source to many later writers such as Strabo and Arrian. He describes such features as the Himalayas and the island of Sri Lanka. He also described India's caste system.