In the Roman calendar, the extra day added between February 23 and 24 every four years, literally meaning 'the sixth day counted twice.'
Latin word meaning 'twice-sixth' (bis = twice, sextus = sixth), referring to the doubling of the sixth day before the March calends. This was the original Roman method of accounting for leap years, predating modern calendar systems.
Ancient Romans were so afraid of changing their calendar numbers that they just counted one day twice instead of inserting a new one—pure bureaucratic genius from people who built aqueducts!
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