The Black Gate is roughly oval in plan and measures 50 feet by 34 feet. It has a central passage (11 feet 6 inches wide) running through it with a vaulted guard room on either side. The northern guard room is semi-circular in plan, whilst the smaller southern guard room's shape is irregular.
Ten feet within the modern
entrance to the passage are grooves for the portcullis and six feet
further reveal a pointed arch rebated on the inside for the main gate.
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