From Stamps of the World
Rotterdam is the second-largest city in the Netherlands and one of the largest ports in the world. Starting as a dam constructed in 1270 on the Rotte River, Rotterdam has grown into a major international commercial centre. Its strategic location at the Rhine-Meuse-Scheldt delta on the North Sea and at the heart of a massive rail, road, air and inland waterway distribution system extending throughout Europe is the reason that Rotterdam is often called the "Gateway to Europe".The largest port in Europe and one of the busiest ports in the world, the port of Rotterdam was the world's busiest port from 1962 to 2004, when it was surpassed by Shanghai. Rotterdam's commercial and strategic importance is based on its location near the mouth of the Nieuwe Maas (New Meuse), a channel in the delta formed by the Rhine and Meuse on the North Sea. These rivers lead directly into the centre of Europe, including the industrial Ruhr region.
Read more at : http://en.wikipedia.org/wiki/Rotterdam