During the Mughal
period, Dhaka became the chief commercial emporium, so much so that forts were
built along the riverbanks to protect the city from Portuguese and Mogh
pirates. In 1626 the Mogh pirates and there Portuguese allies briefly took
Dhaka, and from 1639 to 1659 the capital was moved to Rajmahal, leaving Dhaka
as the administrative centre. This had the effect of encouraging a greater
concentration of commerce; and maritime trade brought with it industry, Islamic
education and increasing sophistication in the arts. As many as 100 vessels
arrived annually to unload their cargo at Narayanganj and to load up with rice,
sugar, fats, oilseeds and wax. Exotic goods were imported from central Asia,
Persia, Afghanistan and Turkey, and the influx of foreign money resulted in
cowries shells being replaced by silver as the local currency.