 The fort was named after James I of England and VI of Scotland, and was built to designs by Paul Ive (to replace and supplement the older medieval structure).Completed by 1607, the central structure was a half-bastioned four-sided stone fortification, surrounded by pentagonal earthworks to a bastion fort or star-shaped fort design.A hexagonal blockhouse was built on the water's edge - a "water battery" at the narrowest point in the channel.