7. Great Tower Neuwerk is the oldest secular building on the German coastline
Built on Neuwerk Island near Hamburg, the Great Tower was originally constructed as a fortification (a keep) in the early 14th century. It was built to house troops who were present to guard the approaches and the estuary of the Elbe from pirates of both the sea and the river. Thus the tower was five centuries old before it was converted to a lighthouse during the Napoleonic era, beginning in 1814. The tower had been part of a navigation system before it became a beacon itself, mariners could take bearings of other beacons and man-made structures as well as the tower to ensure that they were in the channel, safe from the rocks and shoals which mark the waters of the estuary. Fire beacons were used at night near the tower, but the tower itself did not hold a source of light for mariners until 1814.
When it was converted to a lighthouse, the 128 foot tall brick tower used 21 oil lamps to create a beacon, using reflectors. For more than fifty years the lamps were fueled with rapeseed oil. In 1870 the fuel was changed to kerosene. A new Fresnel lens installed in 1892 remains in use, though the light source was changed to electricity in 1942, in part as a defense measure allowing the beacon to be shut down rapidly, rather than allowing it to serve as a guide to incoming Royal Air Force bombers during their night raids. After five centuries as a fortress and two hundred years as a lighthouse the Great Tower was officially shut down. The Hamburg Port Authority continues to shine a small light from the Great Tower, not as a navigational aid but as an attraction for the city. The small light is provided by LEDs.