The drawbridge is a wooden bridge raised up and down to let people in or out of the castle. When enemies try to get into the castle it is raised to stop them from getting in.
Most people know what a drawbridge is. There are three main types: (1) a simple sliding platform over a hole that could be pulled back, (2) a raising bridge pulled up by chains attached to the corners of the drawbridge, and (3) a bridge with posts reaching out over the top, with the chains hanging over the posts.
we got this picture from www.castlexplorer.com