 Work started on 16 April 1805, but a report by Brigadier-General Twiss to the Board of Ordnance in May 1808 recommended that the money to settle Hobson's account be withheld until all the work was completed.The structure was built on a raft of compacted chalk laid directly onto the natural shingle.It was constructed almost entirely of brick, over 50,000 being used in a single course.