Cairo, Egypt, in its history[?] has had a significant number of fortified gates protecting both inner and outer city. Apart from the purpose of defense they were also used for differentiation of the varied social and economic classes. Often the gates were heavily decorated as artistic pieces.
... accelerated to a smaller extent by the slipping friction.
The device is covered by US patents 3,726,146 (1973) and 5,353,655 (1994) by L.A. Mishler and US patent ...