The Arthashastra and the Edicts of Ashoka are the primary written records of the Mauryan times. Archaeologically, this period falls into the era of Northern Black Polished Ware (NBPW). The Mauryan Empire was based on a modern and efficient economy and society. However, the sale of merchandise was closely regulated by the government. Although there was no banking in the Mauryan society, usury was customary. A significant amount of written records on slavery are found, suggesting a prevalence thereof. During this period, a high quality steel called Wootz steel was developed in south India and was later exported to China and Arabia.