Epoch (reference date) in the context of "Byzantine Era"

An olympiad (Greek: Ὀλυμπιάς, Olympiás) is a period of four years, particularly those associated with the ancient and modern Olympic Games.

Although the ancient Olympics were established during Greece's Archaic Era, it was not until Hippias that a consistent list was established and not until Ephorus in the Hellenistic period that the first recorded Olympic contest was used as a calendar epoch. Ancient authors agreed that other Olympics had been held before the race won by Coroebus but disagreed on how many; the convention was established to place Coroebus's victory at a time equivalent to the summer of 776 BC in the Proleptic Julian calendar, and to treat it as Year 1 of Olympiad 1. Olympiad 2 began with the next games in the summer of 772 BC.

The Hijri calendar (Arabic: ٱلتَّقْوِيم ٱلْهِجْرِيّ, romanized: al-taqwīm al-hijrī), also known in English as the Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to determine the proper days of Islamic holidays and rituals, such as the annual fasting and the annual season for the great pilgrimage. In almost all countries where the predominant religion is Islam, the civil calendar is the Gregorian calendar, with Syriac month-names used in the Levant and Mesopotamia (Iraq, Syria, Jordan, Lebanon and Palestine), but the religious calendar is the Hijri one.

This calendar enumerates the Hijri era, whose epoch was established as the Islamic New Year in 622 CE. During that year, Muhammad and his followers migrated from Mecca to Medina and established the first Muslim community (ummah), an event commemorated as the Hijrah. In the West, dates in this era are usually denoted AH (Latin: Anno Hegirae, lit. 'In the year of the Hijrah'). In Muslim countries, it is also sometimes denoted as H from its Arabic form (سَنَة هِجْرِيَّة, abbreviated ھ). In English, years prior to the Hijra are denoted as BH ("Before the Hijra").

The Decline of the West (German: Der Untergang des Abendlandes; more literally, The Downfall of the Occident or even more literally, "The Going-Under of the Evening Lands") is a two-volume work by Oswald Spengler. The first volume, subtitled Form and Actuality, was published in the summer of 1918. The second volume, subtitled Perspectives of World History, was published in 1922. The definitive edition of both volumes was published in 1923.

Spengler introduced his book as a "Copernican overturning"—a specific metaphor of societal collapse—involving the rejection of the Eurocentric view of history, especially the division of history into the linear "ancient-medieval-modern" rubric. According to Spengler, the meaningful units for history are not epochs but whole cultures which evolve as organisms. In his framework, the terms "culture" and "civilization" were given non-standard definitions, and cultures are described as having lifespans of about a thousand years of flourishing, and a thousand years of decline.

The 4th century BC started the first day of 400 BC and ended the last day of 301 BC. It is considered part of the Classical era, epoch, or historical period.

This century marked the height of Classical Greek civilization in all of its aspects. By the year 400 BC Greek philosophy, art, literature and architecture had spread far and wide, with the numerous independent Greek colonies that had sprung up throughout the lands of the eastern Mediterranean.

A regnal year is a year of the reign of a sovereign, from the Latin regnum meaning kingdom, rule. Regnal years considered the date as an ordinal, not a cardinal number. For example, a monarch could have a first year of rule, a second year of rule, a third year of rule, and so on, but not a zeroth year of rule.

Applying this ancient epoch system to modern calculations of time, which include zero, is what led to the debate over when the third millennium began. Regnal years are "finite era names", contrary to "infinite era names" such as Christian era, Jimmu era, Juche era, and so on.

The Era of the Martyrs (Latin: anno martyrum), also known as the Diocletian era (Latin: anno Diocletiani), is a method of numbering years based on the reign of Roman Emperor Diocletian who instigated the last major persecution against Christians in the Empire. It was used by the Church of Alexandria beginning in the 4th century AD and it has been used by the Coptic Orthodox Church of Alexandria from the 5th century until the present. This era was used to number the year in Easter tables produced by the Church of Alexandria.

Diocletian began his reign on 20 November 284 AD, and the reference epoch (day one of the Diocletian era) was assigned to be the first day of that Alexandrian year, 1 Thoth, the Egyptian New Year, or 29 August 284 AD.