Portculli

"The portcullis, which was intended for closing purposes, is described as a flat stone “found sticking up,” which “had never been let down.”[…]The Ante-chamber, or Anti-closet of Mr. Greaves, is fitted on each side with four groves for the reception of portculli or flat stones, to be let down to block up the way to the King’s Room from the Gallery.[…]A boss has been noticed upon this leaf or portcullis. Each groove has a semi-circular top. A French authority makes the whole side to be 9 feet 10 inches long; the width of the groove filled by the portcullis is about 20 inches. Three portculli were thus provided for."