Whatever is unknown is taken for marvelous; but now the limits of Britain are laid bare.

Tacitus writes this in the wake of Rome’s late–first-century campaigns in northern Britain, especially those associated with his father-in-law Gnaeus Julius Agricola, governor of Britain (AD 77–84). In the biography *Agricola*, Tacitus contrasts earlier, rumor-filled imaginings of Britain with the new, hard-won knowledge produced by reconnaissance, marching camps, and naval circumnavigation. The line reflects a Roman imperial mindset: exploration and conquest convert the “marvelous” (what lies beyond the map) into surveyed, describable territory. It also serves Tacitus’ larger purpose of praising Agricola’s achievements while hinting at the costs and moral ambiguities of empire.

The sentence captures a recurring classical idea: ignorance breeds wonder, while knowledge dispels it. Tacitus applies this to geography and empire—Britain once seemed a realm of fable at the edge of the world, but Roman arms and administration have rendered it legible and bounded. The phrase “limits … laid bare” suggests both discovery and domination: to map a place is also to expose it to control. Read more broadly, the line can be taken as a skeptical comment on how “marvels” often shrink under scrutiny, and how power turns the unknown into an object of possession.