In a comment on an earlier post, I pointed out this site, where Stan Wolfson argues for Thule being Shetland. In passing he suggests that Tacitus has awarded Agricola some of the credit for the conquest of Northern Britain that really belongs to Cerialis, one of Agricola's predecessors. In particular see Part Five: Thule in Contemporary Latin Literature.
This is backed up by two reports from The Roman Gask Project, which describes itself as, "A long term programme to study the Roman Frontier works on and around the Gask Ridge in Perthshire, Scotland." One is Archaeology Versus Tacitus, which basically deplores in an amusing fashion the lack of historical knowledge on the part of archaeologists and of archaeological knowledge on the part of historians. The second, Agricola, He Came, He Saw, But Did He Conquer? , informs us of archaeological findings at Gask which suggest the Romans were there earlier than Agricola's governorship.
