Nineteenth century map-makers had a feeling there was something more to the area when they spotted the remains of Iron Age earthworks during an Ordnance Survey expedition.
On opposite sides of the Manawapou River mouth the earthworks of Thacker's and Inman's redoubts can also still be seen and just south of the town the Okautiro redoubt.
Most of these sites survive not as impressive ruins, but as the grassed-over remains of slumped earthworks formerly supporting timber structures.
In many other cases, evidence of masonry features or earthworks allows us to appreciate that the structures of urban castles embodied the architecture of authority.
It is not known whether there were similar earthworks around the southern settlements; archaeology has failed to find clear evidence of such.
Studies show the crabs can also cause serious damage by burrowing into banks and earthworks along rivers.
Some 1400 kilometres of earthworks need to be completed before it can take the ballast, sleepers and rails.
The more powerful it was, the longer and heavier the trains it could pull, but the more substantial its rails and earthworks had to be to carry it.
The castle dates back to c 1180, but is also thought to incorporate earlier Anglo-Saxon earthworks .
Great care was taken as the board envisaged disastrous results if the earthworks collapsed and released a wall of water upon New Plymouth.