millennia

A millennia is a period of 1,000 years. The term derives from Latin mille, meaning thousand, and annus, meaning year. The plural form is millennia, and the adjective form is millennial in some uses.

In historiography, millennia are used to discuss long-term patterns across civilizations. The standard convention for the Common Era places the 1st millennium CE from year 1 to 1000, the 2nd from 1001 to 2000, and the 3rd from 2001 to 3000; there are occasional alternative boundaries because there is no year zero in this calendar system.

Within a millennium there are ten centuries. Historical interpretation often emphasizes broad changes spanning these periods: the 1st millennium includes late antiquity and the spread of Christianity; the 2nd encompasses the Middle Ages, the Renaissance, and the early modern era; the 3rd covers industrialization, globalization, and the digital age that began in the late 20th century. Millennial scales are used to frame long-term trends in areas such as demography, technology, religion, and culture.

In scientific contexts, millennial timescales describe processes and events that unfold over thousands of years, such as climate variability, evolutionary change, and geological or astronomical phenomena. The term can sometimes be confused with millennial as a reference to the generation born around the turn of the 21st century, though in this article it denotes a time span rather than a social cohort.