Although, as explained in the article GENERAL CHRONOLOGY, the monk known as Dionysius Exiguus, when resident in Rome, c.527, seems to have been the first to initiate the practice of calculating years from the birth of Christ and although it was undoubtedly he who identified the year of Christ's birth with the year 753 of the foundation of Rome, as is still done in our current chronology, nevertheless it was not until long after the age of Dionysius Exiguus that the system came into common use.As a rule the charters emanating from the chancery of the Western Emperors are much more liable to this form of error than those of the Holy See (Bresslau, ib., 844). In any case it remains certain and is admitted by all serious writers upon diplomatics that the mere fact that an erroneous date occurs in a document, especially when we are dealing with the earlier Middle Ages, cannot by itself be accepted as a proof, or even a presumption, of the spuriousness of the document.
Taking eight such documents, the eight earliest which we can quote with confidence and dated respectively 679, 692, 697, 732, 734, 736, 740, 759, we may notice says Professor Earle (Land Charters, Introduc., p.
xxxiii) that "of this series the first five though all more or less dated, whether by the month or the regnal year, or by the Indiction, or by all these at once, have not the Anno Domini.
The indiction was a cycle of fifteen years, the first of these cycles being conceived to have started at a point three years before the beginning of the present Christian Era.
It was usual to indicate only the position of the year in the current indiction, and no notice was taken of the number of cycles already completed.
This points no doubt to a time "when ecclesiastics knew the era well enough but had not yet acquired the punctual habit of using it".
It is in any case certain that neither in the papal chancery nor in that of the Western Empire was the system introduced until considerably later.It was the pope's habit to date his letters by the regnal years of the emperor and letters so dated may be seen in Bede's "Ecclesiastical History", just as they were copied from the Roman archives.Apparently it was the Englishman Bede himself who was the first to bring the Dionysian system into general use, for it was through him that it was adopted in literature, having been employed systematically not only in his "De Temporum Ratione" but especially in his "Ecclesiastical History".Thus, for example, meant the fourth year of some particular indiction and not the fourth cycle of fifteen years after B. 3; from which it follows that merely to know the year of the indiction is useless for determining the absolute date of any document unless we know otherwise approximately the period to which the document belongs.In reckoning the beginning and consequently the determining-point of the indiction-cycles four different systems were adopted: the .On the other hand, the last three agree in using the Christian Era and from this time the practice is continuous.