Roman legionaries would have recognised intervallum instantly — it was the measured space between the wooden stakes of their fortifications. The word joins inter ('between') and vallum ('rampart'), capturing a concept that mattered enormously to soldiers whose lives depended on defensive geometry. Latin writers gradually stretched the meaning beyond physical space. Cicero used it for pauses in speech; Seneca applied it to gaps in time. By the time Old French borrowed it as intervalle in the 12th century, both spatial and temporal meanings travelled together. English adopted the word in the 13th century, and the temporal sense steadily gained ground. In music, interval acquired a specialised meaning — the pitch distance between two notes — by the 16th century. Mathematics followed with its own precise definition. The word's journey from military engineering to abstract measurement mirrors how many Latin technical terms evolved: concrete origins gradually giving way to metaphorical extensions that now feel like the primary meaning.