Amsterdam has a long and eventful history. The origins of the city lie in the 12th century, when fishermen living along the banks of the River Amstel built a bridge across the waterway near the IJ, which at the time was a large saltwater inlet. Wooden locks under the bridge served as a dam protecting the village from the rising IJ waters, which often flooded the early settlement. The mouth of the river Amstel, where the Damrak is now, formed a natural harbor, which became important for trading-exchange from the larger koggeships into the smaller ships that sailed the merchandise deeper into the hinterland.