Gauls adapted the system to their own uses, but they renamed
the months and the days of the week aft er their own gods.
Ancient Europeans did not spend much time worry-
ing about the time of day. Th ey might use sundials to give
themselves a rough idea of the time, but they had no me-
chanical clocks, and, like most ancient peoples, they saw
no need for minute-to-minute precision in timekeeping. As
the Romans infi ltrated the continent, Gauls and Germans
adopted Greek and Roman technologies, such as the sun-
dial and the water clock. A sundial was a fl at disc with an
upright piece oriented in such a way that the sun’s light cre-
ated a regular pattern of shadow over the course of a day.
Romans brought sundials with them to Gaul and Britain,
installing them in their home gardens. Aft er the Romans
left , the Europeans kept their timepieces; early medieval
monastery gardens oft en contained sundials installed ac-
cording to the Roman practice.
Th e water clock was a device that allowed people to keep
track of time by measuring the regular fl ow of water into a
stone or metal vessel. Th e water dripped at a constant rate
and gradually fi lled the container; markings in the container
indicated how much time had passed when the water level
reached them. Th is was especially useful for timing the hours
of the night, when the sun was not available to provide visual
clues. Water clocks could at best provide only a rough esti-
mate of the time, and they had to be refi lled constantly with
water in order to work at all. Still, they could provide more
information about time than mere astronomical observation.
For example, when Julius Caesar visited Britain in 55 b.c.e.,
he used a water clock to determine that the nights there were
longer than those on the Continent. Water clocks were valu-
able objects in ancient times; oft en a town would acquire a
single water clock for the entire community.GREECE
BY TOM STREISSGUTH
An accurate measure of the year was important for ancient
societies concerned with the best times for planting and har-
vesting, for observing annual religious festivals, and for re-
cording their own history. Early methods for counting the
days, however, were not precise enough to match the true so-
lar year, meaning that calendars gradually went out of phase
with the seasons. Th e Greek writer Hesiod (ca. 700 b.c.e.), in
his poem Work s and D ays, advises tillers of the soil to reckon
planting and harvest times by the fi rst appearance of stars
in the night sky. Aft er Hesiod’s time the Greeks developed
a more artifi cial system, a lunar calendar of 12 months with
an “intercalary” 13th month inserted when needed to make
up days missing from the lunar year. Calendars changed
somewhat from one Greek city to the next; each had its own
method of fi guring the precise length of the year and the time
to impose the extra month.
Athens, the dominant city of ancient Greece, left behind
the calendar most familiar to historians. Th e months of Ath-
ens had 29 or 30 days, alternating from one month to the
next. Each month was divided into three shorter periods. Th e
fi rst 10 days were those of the “waxing moon.” Th e secondAncient Romans did not use weeks. They marked points in the month by naming specifi c days (calends, ides, nones)
after phases of the moon. They also counted market intervals, but market days were eight days apart, not seven. Eu-
ropeans north of the Mediterranean did not count weeks either, instead letting the moon guide them from night to
night. These systems worked well for centuries, so why did people switch to a seven-day week?
The answer comes from a combination of astrology and Christianity. Ancient Babylonians invented a seven-day
week in 700 B.C.E. They chose the number seven because they knew of seven planets (fi ve modern planets plus the sun
and moon) and believed that each day was controlled by one of these heavenly bodies. They named each day after a
planet. By the fourth century C.E. many Romans had adopted this seven-day system, substituting the names of their
own gods for the Babylonian ones. These names are still visible in three English day names: “Sun” day, “Moon” day,
and “Saturn” day.
When the Roman emperor Constantine converted the Roman Empire to Christianity in 313 C.E., he had to decide
when to celebrate the Sabbath. In 321 he issued an edict declaring an offi cial seven-day week, with the Sabbath on
Sunday. Everyone then knew when they were supposed to rest and worship.
The seven-day week gradually spread through the empire over the next couple of generations. Europeans beyond
the reach of the empire took longer, but even they eventually adopted the seven-day week as the primary unit of time.
By the fi fth century even Anglo-Saxons in Britain were using the week, but they renamed four days after their own
gods. The day that the Romans had named for the war god Mars became “Tuesday,” named for the heroic Germanic
god Tiw. The day the Romans had named for Mercury became “Wednesday,” after the god Wodin. The following day,
named for Jupiter by the Romans, became “Thursday,” for the god Thor. The day the Romans had named for Venus
became Friday, for the goddess Frigga.SEVEN OR EIGHT DAYS A WEEK?
170 calendars and clocks: Greece