Ancient Rome

=== Time and dates ===
{{See also|Roman timekeeping|Roman calendar|Roman consul#Consular dating}}
Roman hours were counted ordinally from dawn to dawn. Thus, if sunrise was at 6 am, then 6 to 7 am was called the "first hour". Midday was called ''[[wikt:meridies|meridies]]'' and it is from this word that the terms ''am'' (''ante meridiem'') and ''pm'' (''post meridiem'') stem. The English word "noon" comes from ''nona'' ("ninth (hour)"), which referred to 3 pm in Ancient Rome.{{Efn|Later in Christian liturgy, "noon" came to describe the [[Nones (liturgy)|nones]], a time of prayer originally at 3 pm but later at midday, so "noon" became synonymous with midday.}} The Romans had clocks (''horologia''), which included giant public [[sundial]]s (''solaria'') and water clocks (''[[Water clock#Greco-Roman world|clepsydrae]]'').

The ancient Roman week originally had eight days, which were identified by letters A to H, with the eighth day being the [[nundinae|nundinum]] or market day, a kind of weekend when farmers sold their produce on the streets. The [[seven-day week]], first introduced from the East during the early Empire, was officially adopted during the reign of [[Constantine the Great|Constantine]]. Romans [[names of the days of the week|named week days]] after celestial bodies from at least the 1st century AD. Roman months had three important days: the [[kalends|calends]] (first day of each month, always in plural), the ides (13th or 15th of the month), and the nones (ninth day before the ides, inclusive, i.e. 5th or 7th of the month). Other days were counted backwards from the next one of these days.

The Roman year originally had ten months from Martius (March) to December, with the winter period not included in the calendar. The first four months were named after gods (Martius, Aprilis, Maius, Junius) and the others were numbered (Quintilis, Sextilis, September, October, November, and December). [[Numa Pompilius]], the second king of Rome (716–673 BC), is said to have introduced the months of January and February, both also named after gods, beginning the 12-month calendar still in use today. In 44 BC, the month Quintilis was renamed to Julius (July) after [[Julius Caesar]] and in 8 BC, Sextilis was renamed to Augustus (August) after [[Augustus Caesar]].

The Romans had several ways of tracking years. One widespread way was the [[Roman consul#Consular dating|consular dating]], which identified years by the two [[Roman consul|consuls]] who ruled each year. Another way, introduced in the late 3rd century AD, was counting years from the [[indiction|''indictio'']], a 15-year period based on the announcement of the delivery of food and other goods to the government. Another way, less popular but more similar to present day, was ''[[ab urbe condita]]'', which counted years from the mythical foundation of Rome in 753 BC.