The Classical WorldScience & Math Julian calendar 45 BCEMajor Caesar adopts a 365.25-day calendar with leap years, used in Europe for 1,600 years. ▲ MattersSaveShareTrace roots Longest chain: The Big Bang → First stars ignite → Supernovae seed heavy elements → The Sun forms → Earth forms → First oceans → First life → Photosynthesis evolves → Great Oxidation Event → Complex cells (eukaryotes) → Multicellular life → First animals → Cambrian Explosion → First vertebrates → Jawed fish → Fish walk onto land → The amniotic egg → The Great Dying → Dinosaurs appear → Asteroid ends the dinosaurs → Early primates → Apes split from monkeys → Human line splits from chimpanzees → Walking upright → First stone tools → Genus Homo appears → Homo erectus → Control of fire → First fired clay figures → First pottery → Potter's wheel → The wheel → Spoke-wheeled chariot → Hittite Empire → Iron Age begins → Rome founded (traditional date) → Roman Republic founded → Caesar crosses the Rubicon → Julian calendar Community notesLoading notes… Learn more ranked by votesDocumentbritannica.comJulian calendar (Britannica) ↗Editor's pickBookDavid Ewing DuncanCalendar: Humanity's Epic Struggle to Determine a True and Accurate Year ↗Editor's pickVideoSearch on YouTubeJulian calendar history ↗Editor's pick