Juvenal mentions these designs (II. 159):
"—Arma quidem ultra
Litora Juvernae promovimus, et modo captas
Orcadas, et minima contentos nocte Britannos" (i.e. those furthest north).
According to Dio Cassius this voyage of discovery was first made by some deserters ('Hist. Rom.' lxix. 20).
The little that is known of this rampart will be found in the next chapter (see p. 198).