Pataliputra 300 BC

“According to report of Megasthenes, a Greek ambassador who visited just before Ashoka was born, the city already covered ten square miles and was surrounded by a wall twenty-one miles long broken by sixty-four gates and 570 towers. This meant it was around twice the size of early Rome, three times the size of Alexandria and eleven times larger than Athens, with a population of some 200,000.” - William Dalrymple, The Golden Road