Work on the new fortification was completed in 1068. Probably at first a wooden keep was constructed, which was later replaced with a much stronger stone one. Lincoln Castle is very unusual in having two mottes, the only other surviving example of such a design being at Lewes. To the south, where the Roman wall stands on the edge of a steep slope, it was retained partially as a curtain wall and partially as a revetment retaining the mottes. In the west, where the ground is more level, the Roman wall was buried within an earth rampart and extended upward to form the Norman castle wall. The Roman west gate (on the same site as the castle's west gate) was excavated in the 19th century but began to collapse on exposure, and so was re-buried.