Basis of chronology : epoch, era, cycle, period

Epocha is derived from the Greek word inhibere, insister, to restrain or limit, and Censorinus calls it not improperly Index or Titulus, as being a fix’d point of time, from whence the part or succeeding progress may be calculated.
Zhra: Sepulvedda de anni emend derives the Word Zhra from a vicious Punctation of A.E R.A. i.e. ANNUS ERAT AVGUSTI; but this Etymology is rejected by Andreas Resndius and Scaliger… As for our part we approve most of their Opinion, who think that by Zhra the Anciennts mean’d a certain Number, commencing from a determined Head.
There ought to be Characters ready at hand whereby an Epocha may be established; else all care will be fruitless: For since Epocha’s, as Scaliger says, are only Notations and Titles of Time: They ought to have proper and distinct Characters.
Cycles comes from the Greek Word Circulus, a Cycle: And every thing, that has an Orbicular Revolution. Is called by this Name. Thus there are Horary, Diurnal, Lunar, Solar, Secular Cycles..
We understand almost the same thing by a Period as by a Cycle ; only we commonly apply the name of a Period to a larger interval of time. A Period differs from an Epoch and an Era, in this, that it includes a Respect to the Terminus ad quem, Whereas these two relate only to the Terminus ad quo. Thus we may justly fay that the present year is the 1664 of the Christian Epoch, But we can not call is such a Year of the Christian Period, because it is not a periodic Epoch.

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From: Strauch, Aegidius, Breviarium chronologicum. Or a treatise describing the terms and most celebrated characters, periods and epocha's [sic] used in chronology. ...

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Historical characters. The historical characters are epochas, or aeras, which are sometimes distinguished from each other, by supposing the epocha to be the head or beginning of any past time, and sera the series, or continuation of years, reckoned from some fixed point, and numbered onwards to an indefinite period. Epocha is, in fact, the Greek term for the point of time from which any reckoning commences, and is still applied to the accounts of years kept by particular cities of Greece, and marked on their medals, [vide Epocha] JEra, which is a term of later invention, is now generally applied to all historical accounts of time that run on in a continued series.
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