Some of these changes were driven by developments in military technology. Before 1190 mining was used rarely and the siege engines of the time were largely incapable of damaging the thicker castle walls. The introduction of the trebuchet began to change this situation; it was able to throw much heavier balls, with remarkable accuracy, and reconstructed devices have been shown to be able to knock holes in walls. Trebuchets were first recorded in England in 1217, and were probably used the year before as well. Richard I used them in his sieges during the Third Crusade and appears to have started to alter his castle designs to accommodate the new technology on his return to Europe. The trebuchet seems to have encouraged the shift towards round and polygonal towers and curved walls. In addition to having fewer or no dead zones, and being easier to defend against mining, these castle designs were also much less easy to attack with trebuchets as the curved surfaces could deflect some of the force of the shot.