Terminus Ante Quem

A Terminus Ante Quem is a point in time before which it has been proven that an event must have occurred. If an undated archaeological artefact is found buried in a layer that is sealed by another layer that contains datable artefacts then the undated artefact must be earlier. Hence a jug found in the earth sealed beneath a wall built in 1400 AD will be earlier than that date and will thus have a Terminus Ante Quem of 1400 AD.

Similarly if a dated document or map mentions a feature that is otherwise undated then the Terminus Ante Quem will be the date of that map or document. So if a map drawn in 1581 depicts a well then that well cannot have been dug after it was depicted.

The opposite concept is known as Terminus Post Quem.