This lonely tower was a favorite subject for Rembrandt, and can be seen either in the background, or as the focus of many of his works. More importantly, the Montelbaanstoren is one of the few pieces of Amsterdam's Medieval walls that still stands. It was a sentinel from which guards could look over the plains for attacking armies. This was often necessary, as Amsterdam was a center of wealth and power at the time, and the frequent target of jealous outsiders. It was the sea that made Amsterdam rich, and this tower guards what was once the greatest shipbuilding complex in the world. It was also a gathering place for sailors before they would go on their long voyages to far-off lands. Today things have changed drastically. Ships are still built in the wharves here, but they're much smaller and don't go very far. Still, the Montelbaanstoren retains its historic link to the sea through its use as office space for the Amsterdam water works. As a side note -- Amsterdam is the last city in The Netherlands to get water meters. Between 2000 and 2030 meters will be installed on all homes and businesses. Previously, water was billed based on the number of rooms in a house, not on consumption.