As with all Roman forts, the defences at the Lunt Roman fort were many and varied. Two V-shaped ditches surrounded the whole fort. These ditches did not contain water, like later castle moats, but wooden stakes and caltrops (metal spikes). In the bottom of the ditches the Romans constructed narrow channels to drain the ditches and to serve as 'ankle breakers' to catch the feet of attackers.
Past the ditches were the fort ramparts. These banks of earth were covered by turf and possibly brambles and nettles making them an unpleasant prospect for those scaling them. If intruders did reach the top of the ramparts, the walls had narrow gaps in them, just wide enough to fit a Roman sword through.
At the Lunt, the defences deviate from the traditional straight line to produce a marked bow shape around the Gyrus on the east side and following the typography of the plateau on the west side.
In 1966, an experimental rampart and ditch section were built. Between seven and ten prisoners from HMP Leicester worked for six hours per day over a twenty day period.
The section which they built in the north-east corner of the fort was 11.27m long and had a timber walkway and crenellated parapet. The rampart had turf walls front and back filled in with earth.
It was estimated from this experiment that to build the whole circuit of ramparts around the fort it would require 138,000 turf blocks and a labour force of 210-300 men working 10 hours per day for 9-12 days.
In the first three years, the reconstructed rampart needed little servicing and it weathered well. The only maintenance necessary was grass cutting. As the earth fill between the inner and outer ramparts settled, the fighting platform sagged slightly and the ditch below filled with silt.
After eight years it was noted that the rampart was still in good condition, though the ditch below had changed from a V-shaped profile to a U-shaped profile despite being cleared of silt every year. Hobley concluded at the end of his experiments that the ramparts could have a long life, possibly lasting decades, and needed little repair.