The portcullis is a heavy metal or wooden (or the combination of the two) grille used to close off a castle entrance. Each portcullis was put in vertical grooves in castle walls and could be raised or lowered by chains or ropes witch were attached to the inside winch. It hangs in the entry to a castle. It can also be lowered to prevent passage.
We got this picture from www.castlexplorer.co.uk