history; and here, as in the Orient,
it is evident that historians of the earlier day were constantly blinded
by a misconception as to the antiquity of civilization. Such a fruitage
as that of Greek culture of the age of Pericles does not come to
maturity without a long period of preparation. Here, as elsewhere, the
laws of evolution hold, permitting no sudden stupendous leaps. But it
required the arduous labours of the archaeologist to prove a proposition
that, once proven, seems self-evident. (H. S. WI.)

_Eras and Periods_.

In the article Calendar (q.v.), that part of chronology is treated which
relates to the measurement of time, and the principal methods are
explained that have been employed, or are still in use, for adjusting
the lunar months of the solar year, as well as the intercalations
necessary for regulating the civil year according to the celestial
motions. But it is necessary to notice here the different _Eras_ and
_Periods_ that have been employed by historians, and by the different
nations of the world, in recording the succession of time and events, to
fix the epochs at which the eras respectively commenced, to ascertain
the form and the initial day of the year made use of, and to establish
their correspondence with the years of the Christian era. These
elements will enable us to convert, by a simple arithmetical operation,
any historical date, of which the chronological characters are given
according to any era whatever, into the corresponding date in the
Christian era.

_Julian Period._--Although the Julian period (the invention of Joseph
Scaliger, in 1582) is not, properly speaking, a chronological era, yet,
on account of its affording considerable facilities in the comparison of
different eras with one another, and in marking without ambiguity the
years before Christ, it is very generally employed by chronologers. It
consists of 7980 Julian years; and the first year of the Christian era
corresponded with the year 4714 of the Julian period.

_Olympiads._--The Olympic games, so famous in Greek history, were
celebrated once every four years, between the new and full moon first
following the summer solstice, on the small plain named Olympia in Elis,
which was bounded on one side by the river Alpheus, on another by the
small tributary stream the Cladeus, and on the other two sides by
mountains. The games lasted five days. Their origin, lost in the dimness
of remote antiquity, was invested by