This Wikipedia page says that the double whole note, or breve, is the "longest note value still in common use".
However, breve in Italian means 'short'.
How did the longest commonly-used note value come to be called 'short'?
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It does mean 'short'. In medieval mensural notation, it was a short note, either one third or half as long as a LONGA. It appears there were only two note lengths, breve and longa from 13th up to the 17th Century, reflecting the syllable sung. The longa is obviously a longer note length... Music may have been much slower then!
Our musical notation evolved over a very long time, during which it became increasingly detailed. This meant that innovation tended to happen at the short end of the time-scale, which probably explains the "inflation" which occurred during the middle ages and early renaissance.
I'm not sure there was ever a time when there were just two values. The story starts with "neumes", which represent whole groups of notes - to the extent that these neumes can be decomposed into individual notes there are many more than two note-shapes, and this visual variety was probably intended to suggest something about the articulation of the notes. In some of the early writings about rhythm the authors can only say that certain notes are "long" and others "short", but this surely reflects the lack of a conceptual framework within which they could speak more precisely rather than implying that only two durations existed.
The idea that a particular note-form (glyph) would exactly correspond to a particular duration (relative to the basic pulse) comes rather late in musical history, and probably only made sense once our ways of measuring and perceiving time had evolved into something close to what we have now. In the 12th century there was no mechanical timepiece which went tick-tock, no unified theory of time which linked musical durations with the hours of the day in one continuum ... there was time, there was music, but there was no 4' 33".