castles, they were spartan, utilitarian constructions. Some historians such as King have disagreed with this interpretation, highlighting the similarities between the two periods, with the historian Christopher Duffy terming the Device Forts the "reinforced-castle fortification". The forts were positioned to defend harbours and anchorages, and designed both to focus artillery fire on enemy ships, and to protect the gunnery teams from attack by those vessels. Some, including the major castles, including the castles of the Downs in Kent, were intended to be self-contained and able to defend themselves against attack from the land, while the smaller blockhouses were primarily focused on the maritime threat. Although there were extensive variations between the individual designs, they had common features and were often built in a consistent style. The larger sites, such as Deal or Camber, were typically squat, with low parapets and massively thick walls to protect against incoming fire. They usually had a central keep, echoing earlier medieval designs, with curved, concentric bastions spreading out from the centre. The main guns were positioned over multiple tiers to enable them to engage targets at different ranges. There were far more gunports than there were guns held by the individual fortification. The bastion walls were pierced with splayed gun embrasures, giving the artillery space to traverse and enabling easy fire control, with overlapping angles of fire. The interiors had sufficient space for gunnery operations, with specially designed vents to remove the black powder smoke generated by the guns. Moats often surrounded the sites, to protect against any attack from land, and they were further protected by what the historian B. Morley describes as the "defensive paraphernalia developed in the Middle Ages": portcullises, murder holes and reinforced doors. The smaller blockhouses took various forms, including D-shapes, octagonal and square designs. The Thames blockhouses were typically protected on either side by additional earthworks and guns. These new fortifications were the most advanced in England at the time, an improvement over earlier medieval designs, and were effective in terms of concentrating firepower on enemy ships. They contained numerous flaws, however, and were primitive in comparison to their counterparts in mainland Europe. The multiple tiers of guns gave the forts a relatively high profile, exposing them to enemy attack, and the curved surfaces of the hollow bastions were vulnerable to artillery. The concentric bastion design prevented overlapping fields of fire in the event of an attack from