Calendar era in the context of "622"

The founding of Rome was a prehistoric event or process later greatly embellished by Roman historians and poets. Archaeological evidence indicates that Rome developed from the gradual union of several hilltop villages during the Final Bronze Age or early Iron Age. Prehistoric habitation of the Italian Peninsula occurred by 48,000 years ago, with the area of Rome being settled by around 1600 BC. Some evidence on the Capitoline Hill possibly dates as early as c. 1700 BC and the nearby valley that later housed the Roman Forum had a developed necropolis by at least 1000 BC. The combination of the hilltop settlements into a single polity by the later 8th century BC was probably influenced by the trend for city-state formation emerging from ancient Greece.

Roman myth held that their city was founded by Romulus, son of the war god Mars and the Vestal virgin Rhea Silvia, fallen princess of Alba Longa and descendant of Aeneas of Troy. Exposed on the Tiber river, Romulus and his twin Remus were suckled by a she-wolf at the Lupercal before being raised by the shepherd Faustulus, taking revenge on their usurping great-uncle Amulius, and restoring Alba Longa to their grandfather Numitor. The brothers then decided to establish a new town but quarrelled over some details, ending with Remus's murder and the establishment of Rome on the Palatine Hill. The year of the supposed founding was variously computed by ancient historians, but the two dates seeming to be officially sanctioned were the Varronian chronology's 753 BC (used by Claudius's Secular Games and Hadrian's Romaea) and the adjacent year of 752 BC (used by the Fasti and the Secular Games of Antoninus Pius and Philip I). Despite known errors in Varro's calculations, it is the 753 BC date that continues to form the basis for most modern calculations of the AUC calendar era.

The terms anno Domini (AD) and before Christ (BC) are used when designating years in the Gregorian and Julian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord" but is often presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ". The form "BC" is specific to English, and equivalent abbreviations are used in other languages: the Latin form, rarely used in English, is ante Christum natum (ACN) or ante Christum (AC).

This calendar era takes as its epoch the traditionally reckoned year of the conception or birth of Jesus. Years AD are counted forward since that epoch and years BC are counted backward from the epoch. There is no year zero in this scheme; thus the year AD 1 immediately follows the year 1 BC. This dating system was devised in 525 by the Eastern Roman monk Dionysius Exiguus but was not widely used until the 9th century. Modern scholars believe that the actual date of birth of Jesus was about 5 BC.

Year 404 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Volusus, Cossus, Fidenas, Ambustus, Maluginensis and Rutilus (or, less frequently, year 350 Ab urbe condita). The denomination 404 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Year 403 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Mamercinus, Varus, Potitus, Iullus, Crassus and Fusus (or, less frequently, year 351 Ab urbe condita). The denomination 403 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.

The moment of epoch is usually decided by congruity, or by following conventions understood from the epoch in question. The epoch moment or date is usually defined from a specific, clear event of change, an epoch event. In a more gradual change, a deciding moment is chosen when the epoch criterion was reached.

An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.

Comparable terms are Epoch, age, period, saeculum, aeon (Greek aion) and yuga (Sanskrit युग).

The Hijri era (Arabic: التقويم الهجري, romanized: at-taqwīm al-hijrī) is the calendar era used to record dates in the Islamic world. Its epoch (start point of the era) is the year in which Muhammad and his followers migrated from Mecca to Yathrib (now Medina), in 622 CE. This event, known as the Hijrah, is commemorated in Islam for its role in the founding of the first Muslim community (ummah). Time in this era is measured by two principal calendars: the lunar Hijri calendar (known in the West as the "Islamic calendar") which counts lunar years since the Hijrah and which is used by most Muslims around the world; and the solar Hijri calendar (also known as the "Persian calendar") which counts solar years since the Hijrah and which is used in Iran.

In the West, dates in the lunar Hijri calendar are denoted as AH (Latin: Anno Hegirae) or Hijri year (Arabic: سنة هجرية, romanized: sanat hijriyya, lit. 'in the year of the Hijra') in the style of the Christian/Common (AD/CE) and Jewish eras (AM) and can similarly be placed before (preferably) or after the date. In predominantly Muslim countries, it is also commonly abbreviated H ("Hijra") from its Arabic abbreviation hāʾ (هـ). Years prior to AH 1 are reckoned in English as BH ("Before the Hijra"), which follows the date. Dates in the solar Hijri calendar are denoted as SH. The current year according to the lunar Hijri calendar is AH 1447; according to the solar Hijri calendar the current year is SH 1404. The difference in numbering arises because a lunar year is about eleven days shorter than a solar year.