THE GREEKS from an early period recognised two natural and cyclic intervals of time: a lunar month of about 29 1/2 days and a solar (seasonal) year of about 365 1/4. Their calendars represented attempts to combine the two; but neither twelve lunar months, amounting to 354 days, nor thirteen lunar months, amounting to 384 days, would disguise the incompatibility of the two systems. Thus artificial cycles were devised, e.g., an octaeteris in which three years were intercalary (i.e., of thirteen months). In 432 B.C. the Athenian astronomer Meton constructed a nineteen-year cycle, in which seven years were to be intercalary. Of the 235 months, 125 were to be full (of 30 days each) and 110 hollow (of 29 days each); the error over the period is less than ten hours. Minor adjustments were introduced later (by Kallippos and Hipparchos) but it is with Meton's cycle that students of the Athenian calendar must primarily contend. A further complication, which aids and also bedevils scholars, is that the Athenians simultaneously, at least from the time of Kleisthenes, employed a conciliar calendar for administrative purposes; that is, each prytany in the Council of Five Hundred served as a sub-committee for (down to 307/6) a tenth part of the Council's term of office, which, in the fifth century, corresponded roughly to a solar year. Public documents were generally dated by the day and number of the prytany (its order of tenure was determined by lot) as well as by the day of the lunar month. The resulting equations, which, to be sure, are few down to about 350 B.C., are fundamental to reconstruction of the Athenian calendar.' Modern study of the subject, especially on this side of the Atlantic, began in 1928 with the publication by Benjamin Dean Meritt of The Athenian Calendar in the Fifth Century Based on a Study of the Detailed Accounts of Money Borrowed by the Athenian State I.G. J,2 324 (Harvard University Press). Meritt, in collaboration with Allen B. West, had already developed and applied new critical methods to an examination of the Athenian tribute-records cut on stone;2 now his indispensable contribution was to reconstruct IG 1.2 324 and to produce, for the first time, an intelligible text. He also proposed, at least as a working hypothesis, a means of calculating interest, rate of interest, and principal. From his results he extracted a number of calendric equations.