 The tower is believed to be an experiment in improving flanking fire by making more ground visible from the summit of the keep.Although unique to England, the design of the tower closely resembles that at Étampes in France, and may have influenced the design of the future keep of Pontefract Castle.Henry employed master mason Henry de Rayns and chief carpenter Simon of Northampton for the project, and the cost of the tower accounted for the majority of the overall expenditure on the castle during this period of work.