The simplest and most primitive type of cal endar was the lunar calendar based on the phases of the moon. The basis was the lunar month of 29 and one-half days. From this it was possible to provide toughly for convenient units of measurement, both longer and shorter than the month: The lunar fortnight was a widespread unit of time, and weeks were se cured from the quarters of the moon or from a division of the months into three periods of 10 days each, the latter being closest mathemat ical solution. Twelve lunar months produced a lunar year of 354 days, and to keep the months synchronized with the seasonal divisions, a thir teenth month was interpolated at appropriate intervals. A longer interval was the lunar cycle of about 19 years, which came into use among the Greeks about 750 n.c. Though the lunar calendar provided no exact divisions of time, either long or short, and was continually getting out of adjustment, it was tolerated and re tained by all the peoples of antiquity except the Egyptians, who share with the aboriginal in habitants of Mexico the honor of having first evolved the solar year and the beginnings of the modern' calendar. The agricultural life of the dwellers in the Nile valley and the importance of the Sun-God in Egypt tended to increase the importance of the sun at the expense of the moon. Accordingly, as early as 4241 a.c., the earliest fixed date in history, the Egyptians had devised a solar year of 365 days, with 12 months of 30 days each and five feast days at the end of each year. The seven-day week of the mod ern calendar, cutting through both month and year, was the product of the ingenuity and reli gious arrangements of the Hebrews. As early as 238 a.c. Alexandrian scientists had devised the quadrennial leap year, and during the Hel lenistic period the Hebrew week was adapted to form the planetary week of the modern cal endar. In 46 a.c. Julius Casar prescribed for the Roman world this solar year, but the planetary week did not come into general use in. Rome before the 2d century A.D. The final step in perfecting the calendaf was taken by the authority of Pope Gregory XIII in 1582.
Eleven days were dropped from the calendar and centennial years were regarded as leap years only when divisible by 400.
The provision of some sort of a crude cal endar was an essential prerequisite of systematic history, but the process had to be carried on a step further before the mechanism for measur ing and recording time was sufficiently perfected to be of any considerable service to the histo rian. It was not enough to be able to measure time by the year and its fractions; it was neces sary to have some method of identifying suc cessive years, in other words, to provide a chronology. While the Egyptians had an ad mirable instrument for fashioning a scientific chronology in the astronomical 'Sothic cycle' of 1461 years, they made no use of it and never provided a scientific chronology. The earliest Egyptian approximation to a chronology was the annalistic expedient of naming the years by some great event which happened therein. The famous °Palermo Stele' constitutes the earliest remaining record of these year-lists and is sup posed, in its original complete form, to have identified the seven hundred years from 3400 a.c to 2700 B.C. An advance in methodology was made when the years were named from the regnal years of a particular king. The only great list of Egyptian regnal years which has been preserved, even in a fragmentary condi tion, is the precious 'Turin Papyrus,» which has to be supplemented by the lists inscribed on the temple walls of the later dynasties. About 275 B.C. Ptolemy Philadelphus commissioned a learned Egyptian priest, Manetho, to collect and translate into Greek all the Egyptian annals and regnal lists. The fragmentary remains of the labors of Manetho have constituted the skeleton upon which modern Egyptologists have recon structed the chronology of ancient Egypt. The
Babylonians never passed beyond the annalistic stage of chronology — namely, the identifying of years by some conspicuous occurrence. A contemporary of Manetho, Berossos, a Babylo nian priest at the court of Antiochus II, tried to do for Babylonian chronology what Manetho had done for Egyptian, but to judge from what remains of his work in the fragments of copy ists, he seems to have been less successful. A far greater exactness was given to Assyrian chronology by the fact that the years of a given king were identified by the annual appointment of an official known as a limmic. As the name of the contemporary limmu was given in the notices of events contained in the clay records, the lists of limmi, dating from 892 a c. to 704 a.c., enable the historian to establish with a high degree of accuracy the Assyrian chronology. In the later period of Assyrian and Babylonian his tory there developed some conception of an Gera,» which dated from the reign of Nabonassar, 747 B.C. The Hebrew chronology never developed further than the crude genealogical system of reckoning by generations, the conventional length of which was 40 years. Some vague con ception of eras seems also to have arisen, as, for example, the period from Abraham to David, or from David to the 'captivity." The classic examples of the Hebrew chronological system are to be found in the opening of the first hook of Chronicles and in the first chapter of Matthew. The early Greek historians, in spite of an admirable starting point for the Greek era in the semi-mythical siege of Troy and an unusually ingenious mechanism for measuring time in the °Cycle of Meton,» no better than their predecessors in creating a chronology. Down to the middle of the 5th century a.c. the only chronological records pos sessed by the Greeks were the local genealogies and the names of archons, priests and priest esses. The early attempt of Hellanicns of Lesbos, in the latter half of the 5th century a.c., to fashion a chronology from genealogies and name lists has been described by Bury as °an ingenious edifice erected on foundations that had no solidity," but even the attempt had some significance. Neither Herodotus nor Thucydides made any attempt at solving the problem of chronology, and the later Greek his torians finished their work with no more satis factory system of chronology than the clumsy method of reciconing by Olympiac years intro duced by Timieus about 300 B.C. The Olympic «ere was dated from the alleged Olympic games in 776 a.c. The laudable effort of Era tosthenes, about 80 years after Timmus, to put Greek chronology on the firm basis of astro nomical measurements was little utilized or en couraged by the historians, though the astro nomical researches of the Alexandrian scientists were of the utmost importance for the future of chronology. The practical minded Romans were the first people of antiquity to devise a rational and reliable system of chronology. They dated their
from the mythical foun dation of Rome in 753 B.C. The monstrosities of the Christian chronology introduced by Julius Africanus, Eusebius and Jerome, as well as the real foundations of modern scientific chro nology with Scaliger's