Fortifications are militaryconstructions designed for defensivewarfare. They have been used for many thousands of years, in a variety of increasingly complex designs. The practice of improving an area's defense is also known as "fortification". Many military installations are known as forts, although they are not always "fortified".
... "rolling" point, but the gyro will also be accelerated to a smaller extent by the slipping friction.
The device is covered by US patents 3,726,146 (1973) and ...