Kassel's medieval fortifications were extensive, but as soon as defence technology advanced beyond cannonballs, they were a hindrance to the city's development and most moats, walls and towers were removed in the 18th century. The elegant Druselturm from 1415 was the tallest tower along the city wall, 44 metres high and leaning slightly, although unfortunately not leaning enough to gain international traction and a cavalcade of tourists propping it up in ‘hilarious’ photos.