During the reign of Emperor Asoka in the 3rd century BCE, it was one of the world's largest cities, with a population of 150,000–300,000. Pataliputra reached the pinnacle of prosperity when it was the capital of the great Mauryan Emperors, Chandragupta Maurya and Ashoka the Great. The city prospered under the Mauryas and a Greek ambassador Megasthenes resided there and left a detailed account of its splendour, referring to it as "Palibothra". The city also became a flourishing Buddhist centre boasting a number of important monasteries. It remained the capital of the Gupta dynasty (3rd–6th centuries) and the Pala Dynasty (8th-12th centuries). The city was largely in ruins when visited by Hsüan-tsang, and suffered further damage at the hands of Muslim raiders in the 12th century. Afterwards, Sher Shah Suri made Pataliputra his capital and changed the name to modern Patna.
Though parts of the ancient city have been excavated, much of it still lies buried beneath modern Patna. During the Mauryan period, the city was described as being shaped as parallelogram, approximately 1.5 miles wide and 9 miles long. Its wooden walls were pierced by 64 gates. These were thought to have been converted to strong stone walls during the time of Ashoka.
The etymology of Pataliputra is unclear. "Putra" means son, and "pāţali" is a species of rice or the plant Bignonia suaveolens. One traditional etymology holds that the city was named after the plant. Another tradition says that Pāṭaliputra means the son of Pāṭali, who was the daughter of Raja Sudarshan. As it was known as Pāṭali-grama originally, some scholars believe that Pāṭaliputra is a transformation of Pāṭalipura, "Pāṭali town".