The ancient Egyptians began numbering their years when the Star Sirius rose at the same place as the Sun. The Egyptian calendar was the first solar calendar and contained 365 days. These were divided into 12 30-day months and five days of festival (Neugebauer 1969). From astronomical calculations, Sirius and the Sun coincided in 4241 and 2773 BC, so either of these could have served as Egyptian Year 1.

The calendar used by the ancient Greeks was based on the Moon, and is known as the Metonic calendar. This calendar was based on the observations of Meton  of Athens (ca. 440 BC), which showed that 235 lunar months made up almost exactly 19 solar years. This 19-year cycle became known as the Metonic Cycle. However, given a nominal twelve-month year, an additional  lunar months needed to be added to synchronize the cycle. These were added in years 3, 5, 8, 11, 13, 16, and 19 of the cycle. Around 325 BC, Callippus  modified the calendar by noting that 4 19-year Metonic cycles with 940 months were very close to 27,759 days. This is called the Callipic Cycle. Hipparchus  noted that an even more accurate cycle (now called the Hipparchic Cycle) consisted of four Callipic Cycles less a day, in which  days were very nearly 3760 months. However, neither system was widely used. A lunar-based calendar is still used by some religious sects to determine holidays. Easter, for instance, generally occurs on the first Sunday following the first Full Moon after the Vernal Equinox, although the actual scheme is a bit more complicated still (Montes).

Prior to 46 BC, the Roman Calendar, or what has been reconstructed of it, is described as a ``mess.'' The Romans calendar originally started the year with the Vernal Equinox and consisted of 10 Months (Martius, Aprilis, Maius, Junius, Quntilis, Sextilis, September, October, November, and December) having a total of 304 days. The numbers still embedded in the last four Months of the year are the fossil of this (September, October, November, and December, contain the Latin roots for the numerals seven, eight, nine, and ten, but now fall on the ninth, tenth, eleventh and twelfth months of the year). The 304 days were followed by an unnamed, unnumbered period in winter. The Roman emperor Numa Pompilius (715-673 BC) introduced February and January between January and March, increasing the length of the year to 354 or 355 days. Then in 450 BC, February was moved to its current position.

In the year 46 BC, the Greek Sosigenes  convinced Julius Caesar to reform the calendar to a more manageable form. The Julian Calendar consisted of cycles of three 365-day years followed by a 366-day Leap Year.

 

The names of the days are in some cases derived from Teutonic deities or, such as in Romance languages, from Roman deities. The early Romans, around the first century, used Saturday as the first day of the week. As the worshipping of the Sun increased, the Sun's day (Sunday) advanced from position of the second day to the first day of the week (and saturday became the seventh day).

Sunday
The name comes from the Latin dies solis, meaning "sun's day": the name of a pagan Roman holiday. It is also called Dominica (Latin), the Day of God. The Romance languages, languages derived from the ancient Latin language (such as French, Spanish, and Italian), retain the root.
French: dimanche; Italian: domenica; Spanish: domingo
German: Sonntag; Dutch: zondag. [both: 'sun-day']

Monday
The name comes from the Anglo-Saxon monandaeg, "the moon's day". This second day was sacred to the goddess of the moon.
French: lundi; Italian: lunedi. Spanish: lunes. [from Luna, "Moon"]
German: Montag; Dutch: maandag. [both: 'moon-day']

Tuesday
This day was named after the Norse god Tyr. The Romans named this day after their war-god Mars: dies Martis.
French: mardi; Italian: martedi; Spanish: martes.
The Germans call Diensdag (meaning "Assembly Day"), in The Netherlands it is known as dinsdag, in Danmark as tirsdag and in Sweden tisdag.

Wednesday
The day named to honor Wodan (Odin).
The Romans called it dies Mercurii, after their god Mercury.
French: mercredi; Italian: mercoledi; Spanish: miércoles.
German: Mittwoch; Dutch: woensdag.

Thursday
The day named after the Norse god Thor. In the Norse languages this day is called Torsdag.
The Romans named this day dies Jovis ("Jove's Day"), after Jove or Jupiter, their most important god.
French: jeudi; Italian: giovedi; Spanish: el jueves.
German: Donnerstag; Dutch. donderdag. [both "thunder day"]

Friday
The day in honor of the Norse goddess Frigg.
In Old High German this day was called frigedag.
To the Romans this day was sacred to the goddess Venus, and was known as dies veneris.
French: vendredi; Italian: venerdi; Spanish: viernes.
German: Freitag ; Dutch: vrijdag.

Saturday
This day was called dies Saturni, "Saturn's Day", by the ancient Romans in honor of Saturn. In Anglo-Saxon: sater daeg.
French: samedi; Italian: sabato; Spanish: el sábádo.
German: Samstag; Dutch: zaterdag.
Sweden: Lördag, and in Danmark and Norway Lørdag ("washing day").