Hadean
The Hadean () is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the ICS, 4 billion years ago. , the ICS describes its status as ""informal"". Geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term, the "Priscoan period", from "priscus", the Latin word for "ancient". Other, older texts simply refer to the eon as the Pre-Archean.
Classical Greece
This century is essentially studied from the Athenian outlook because Athens has left us more narratives, plays, and other written works than the other ancient Greek states. From the perspective of Athenian culture in Classical Greece, the period generally referred to as the 5th century BC extends slightly into the 4th century BC. In this context, one might consider that the first significant event of this century occurs in 508 BC, with the fall of the last Athenian tyrant and Cleisthenes' reforms. However, a broader view of the whole Greek world might place its beginning at the Ionian Revolt of 500 BC, the event that provoked the Persian invasion of 492 BC. The Persians were defeated in 490 BC. A second Persian attempt, in 481–479 BC, failed as well, despite having overrun much of modern-day Greece (north of the Isthmus of Corinth) at a crucial point during the war following the Battle of Thermopylae and the Battle of Artemisium. The Delian League then formed, under Athenian hegemony and as Athens' instrument. Athens' excesses caused several revolts among the allied cities, all of which were put down by force, but Athenian dynamism finally awoke Sparta and brought about the Peloponnesian War in 431 BC. After both forces were spent, a brief peace came about; then the war resumed to Sparta's advantage. Athens was definitively defeated in 404 BC, and internal Athenian agitations mark the end of the 5th century BC in Greece.