The iron gate at the drawbridge?

The paint is applied to form a protective barrier between the iron gate and the weather. This is to prevent the iron from oxidising (rust) and corrodin, also on a more pleasant note, it looks nice

Iron rusts quite quickly when exposed to the environment, so painting them protects the iron from corrosion.

An iron gate that moved vertically was called a portcullis.

The Iron Gate. This is a gorge on the Danube between Romania and Serbia. A dam and major hydroelectric project were completed near there in 1972. In the process an island in the Danube called...

The mass increases until the rust flakes off,which leaves less original mass. Eventually the gate will rust completely away.