These were heavy, vertically opening gates - most typically found in medieval fortresses. They were made of either wood or metal (or a combination of the two). They were designed to provide a way to quickly close a door (or similar entrance), to stop entry. Doorways and windows would have grooved slides fitted into their construction. Lowered and raised by a series of pulleys or gears (using chain and rope). The open lattices afforded Archers and Crossbowmen the ability to fire and still retain some protection.