Rotterdam ( /ˈrɒtərdæm/; Dutch [ˌrɔ.tər.ˈdɑm] ) 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".