In 1634, the Dutch West India Company (W.I.C.) founded a trading post at St. Anna's Bay on the island of Curacao. This sheltered bay formed a natural harbour. From about 1660, the slave trade took off. Willemstad was a centre of the slave trade for the whole of the Americas. The town developed continuously over the following three centuries on both sides of the Saint Anna Bay to become a Caribbean harbour city. Willemstad is characterised by a mix of architectural styles and Caribbean colours. There are many Dutch influences, but also Spanish and Portuguese. The historic town centre of Willemstad has been a World Heritage site since 1997.