revolution around the sun were not counted, since the calen-
dar was based on the agricultural cycle, the Romans had no
need to measure the winter months.
Early Roman calendars kept pace with the sun by pe-
riodically adding a month of 27 days aft er February, at the
discretion of the pontifex maximus, a priest who was ap-
pointed by the emperor and oft en wielded his control over
the calendar for political reasons. By the sixth century b.c.e.
the Romans changed to the 12-month calendar, with a total
of 355 days per year. Th is still was not in accordance with
the earth’s revolution around the sun, which was later mea-
sured as taking 365.25 days per year, but it was close. By
the time of Julius Caesar (100–44 b.c.e.), the calendar was
about three months ahead of the earth’s natural revolution
around the sun.
Th e Julian calendar, instituted in 46 b.c.e., revised the
calendar into what has become the standard for Western civi-
lization. Starting in January of 45 b.c.e. the year was estab-
lished at 365 days, with an extra day added every fourth year.
Th e Julian calendar was out of sync with the earth’s revolu-
tion by only about 11 minutes each year. Since Caesar’s time,
the only signifi cant change has been the Gregorian calendar,
commissioned by Pope Gregory XIII in 1582: It removed 10
days that year and included provisions to keep extra days
from building up in the future by removing three days every
400 years. Th is was accomplished by skipping leap year in
years that are divisible by 100 (but not by 400), so that Febru-
ary of 1700, 1800, and 1900 did not have the extra leap-year
day added, while February of 2000 did. Th e Julian calendar
was so infl uential, though, that it was still followed in Britain
until 1751.
Romans did not count the days continuously through
the month until it ended. Instead, they broke the month
into three separate sections. Th e fi rst day of each month was
Kalands; the Nones, originally the day on which the moon
reached its fi rst quarter phase, was the designation for the
seventh day of some months (March, May, July, and Oc-
tober) and the fi ft h day of the rest; and the Ides, based on
the time of the full moon, was the 15th day of those same
months and the 13th of the others. Days were measured
counting up to the next demarcation. Th e third of March,
for instance, would be “5 before Nones March” (V ante diem
Non. Mar.): the Romans counted inclusively, so their tally
would include the number they were counting toward. Th e
10th of March would be “6 before Ides March” (VI a.d. Ides
Mar.), and the 20th of March would be “12 before Kalands
April” (XII a.d. Kal. Apr.).
Ancient Romans were quite familiar with many of the
methods we use today to measure time, even though they did
not feel the need to be as precise about time as we are in the
modern world. Th e Romans did not divide the day into 24
equal hours but instead divided it into two halves, with 12
night hours and 12 day hours. Th e duration of these hours
varied as the year changed, except at the two equinoxes, when
day and night are the same length. In winter, when the days
are shorter, a daytime hour could be as short as 45 minutes,
while in the middle of the summer, when daylight lasted lon-
gest, a daytime hour could be as long as one and a half of
our hours. In addition to being aff ected by the seasons, the
lengths of sunlight hours also varied across the Roman Em-
pire according to one’s longitudinal position.
In the Roman day “fi rst hour” was the hour follow-
ing sunrise. “Midday” was the sixth hour aft er sunrise,
“12th hour” the hour before sunset, and midnight the sixth
hour of the night. Hours were marked with sundials or, in
wealthy households, with water clocks. Anything occurring
before midday was referred to as ante meridiem, which is
used today by its common abbreviation “a.m.”; anything af-
ter midday was called post meridiem, or “p.m.” While this
system of dividing the day was consistent across the empire,
the Romans were far less skillful at measuring units of time
within an hour. At fi rst there was no attempt to measure
time in shorter increments than the hour. In 263 b.c.e. the
fi rst sundial was brought to Rome from Sicily, as part of the
treasure gained in the fi rst Punic War (264–241 b.c.e.). It
was not calibrated for the Roman sun and was therefore un-
reliable. Eventually someone realized that the problem was
not just with the Sicilian sundial, constructed for a diff erent
latitude, but indeed with all sundials, which could not be
adjusted for accuracy as the earth changed its position rela-
tive to the sun during the year.
In 159 b.c.e. the water clock was imported from Greece.
Th is clock measured time according to how much water
dripped through a narrowed opening in a measured span. Be-
cause it did not rely on the sun, a water clock’s measurement
could remain constant throughout the year. Th is benefi t,
however, was also a weakness: without any universal source
such as the sun for reference, it was very unlikely that the
time measurements of any two water clocks were consistent
with each other. Ancient Rome was instrumental in devising
a calendar that could follow the earth’s revolution around the
sun, but the Romans were never very accurate about measur-
ing units of time within the days.THE AMERICAS
BY ANGELA HERREN
Many inhabitants of the ancient Americas developed so-
phisticated methods of marking time based on careful ob-
servation of natural and astronomical phenomena. While
the archaeological record in North America provides no
evidence of calendar and clock use, simple farming began
around 100 b.c.e., suggesting a basic knowledge of seasonal
cycles. In Mesoamerica and South America the alignment
and orientation of many pre-Hispanic buildings and archae-
ological sites acknowledge the rotation and movements of the
sun, moon, and stars. Painting, sculpture, and portable arts
oft en refl ected ritual activities designed to promote success
in seasonal agriculture. In ancient Mesoamerica the Maya
and their predecessors developed sophisticated 260-day and172 calendars and clocks: The Americas