clifford's tower is of an unusual design. the two-storey tower has a quatrefoil plan with four circular lobes. each lobe measures 22 feet (6.5 metres) across, with walls 9 feet 6 inches (3 metres) thick; at its widest, the tower is 79 feet (24 metres) across. a square gatehouse, 21 feet (6.5 metres) wide, protected the entrance on the south side between two of the lobes. there are defensive turrets between the other lobes. large corbels and a central pier supported the huge weight of stone and the first floor. loopholes of a design unique to york castle provided firing points. a chapel was built over the entrance, measuring 15 feet by 14 feet (4.5 metres by 4.2 metres), doubling as a portcullis chamber as at harlech and chepstow castles. 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.