Pataliputra was an ancient city founded in 490 BCE by the king of Magadha-Ajatashatru. His son Udaya made it the capital of Magadha, which it remained until the 1st century BCE. It was also the capital of Chandragupta Maurya. After Ajatashatrus demise, his son and successor, Udayin, taking into account Pataliputras strategic importance, shifted the Magadhan capital from Rajgir to the city newly fortified by his father. It was not only central to important provinces but its location made it easy to connect Pataliputra by road to several other important cities like Mathura in the west, Tamralipti in the east, also Allahabad, Benaras, Punjab, and Delhi. 

Accounts of travelers

Fa-Hien

The Chinese pilgrim Fa-Hien, who visited Pataliputra in 399-414 BCE, mentioned the elegant carving and inlay wood sculpture work of the buildings, in a way that no human hands of this world could accomplish. He stayed and studied here for three years.^[ref]

Megasthenes

Megasthenes, ambassador of the Greek ruler Seleucus I Nicator in the court of Chandragupta Maurya (reign c. 321 c. 297 BCE), in his book Indica wrote that Pataliputra was among the first cities in the world to have a highly efficient form of local self-government.^[ref]

Strabo

The Greco-Roman geographer Strabo in his book Geographia, writes, At the confluence of the Ganges and another river is situated Palibothra (as the Greeks called Pataliputra), in length 80, and breadth 15 stadia. It is in the shape of a parallelogram, surrounded by a wooden wall pierced with openings through which arrows may be discharged. In front is a ditch, which serves the purpose of defense and a sewer for the city. The wall was crowned with 570 towers and had 46 gates!^[ref]

Xuan Zang

Of the many Chinese Buddhists who came to India, Xuanzang was the traveler best remembered for the extensiveness of his forays across India, ranging from Kashmir and Punjab to Bihar, Assam, and the peninsula. Wherever he went, he recorded his observations on monasteries, ruined cities, stupas, the myths surrounding them, and a great deal else. Xuanzangs account of Pataliputra is marked by most of these features. It is part observation and a part amalgam of legends. Upon leaving Vaishali and crossing the Ganga, this restless and intrepid pilgrim reached Pataliputra. Located on the holy river's right bank, the city he said was one that had, many centuries earlier, been created there as the new capital of Magadha by Ashokano doubt he had been told this or gleaned it from existing legend. Contrary to what Xuanzang believed, however, Pataliputras establishment as Magadhas capital did not have anything to do with Ashoka, and the Chinese pilgrim may have been confusing Bindusara with Bimbisarathe latter, at any rate, had no relationship of any kind with Ashoka. By the time of Xuanzangs visit, his account suggests, the Magadha realm included towns that were well peopled, whereas the old city of Pataliputra was a somewhat unimpressive and decaying settlement, one that he characterized as having long been a wilderness whose foundation walls had survived. By this Xuanzang probably meant that the ruins of earlier buildings were still visible within the city. He had encountered such ruins in many places across India before, but, exceptionally in the case of Pataliputra, the visible traces of stupas, pillars, old towers, and strange stones seemed to him to be closely associated with Ashoka.^[ref]