East Germans successfully defected by a variety of methods: digging long tunnels under the wall, waiting for favorable winds and taking a hot air balloon, sliding along aerial wires, flying ultralights, and in one instance, simply driving a sports car at full speed through the basic, initial fortifications. When a metal beam was placed at checkpoints to prevent this kind of defection, up to four people (two in the front seats and possibly two in the boot) drove under the bar in a sports car that had been modified to allow the roof and wind screen to come away when it made contact with the beam. They lay flat and kept driving forward. The East Germans then built zig-zagging roads at checkpoints. The sewer system predated the wall, and some people escaped through the sewers, in a number of cases with assistance from the Girmann student group.