It is to be noted that in the Liber Armachanus two divergent subputations of Patrick’s age are found. One of these was originally appended to the exemplar of Muirchu which was used by the Armagh scribe; the other is among the notes which are appended to his transcription of Tírechán.
In the first (300₂₁) it is stated that Patrick, having been captured in his 20th year, was a slave for 15 years, studied for 40, and taught for 61. Hence it is inferred that his age was 111. There must be errors in the figures.
In the second (331₂₂) we have the following statement:—baptized in 7th year, captured in 10th, was a slave for 7 years, studied for 30 years, and taught for 72. Hence his age at his death is inferred as 120 (10 + 7 + 30 + 72 = 119), ut Moyses.
It is, I venture to think, of the greatest significance that in both these cases the fictitious age is given as a total, and preceded by a statement of the items which compose it. This fact furnishes the clue. The Mosaic age, 120, was not handed down as a legend, nor was the true age of somewhat over 70 audaciously raised to the Mosaic figure for the purpose of the Mosaic comparison. The figure 120, or something approximate, was reached by means of a computation of chronological items, and it is these chronological items that we must examine in order to discover the origin of the error.
In the two anonymous computations which I have quoted the items disagree with each other, and also disagree with the data in Patrick’s Confession. They cannot therefore form the basis of our examination, because we may safely assume that the computation, by which 120 years (exactly or approximately) was reached and was generally accepted in Ireland, did not contravene the data of the Confession—data which were rightly quoted in Tírechán (302₁₇) from the Book of Ultan. We may safely assume that the computators, who succeeded in establishing the Mosaic age, started with the incontrovertible fact supplied by the Confession that Patrick was either 22 years old, or in his 22nd year, when he escaped from captivity. It is equally clear that the period which they assigned to his teaching was 60 (rather 61 years)—for that is the period from his arrival in Ireland, A.D. 433 (rather 432) to the alleged date of his death, A.D. 493. This would leave 38 (rather 37) years to be accounted for. Now Muirchu mentions two different records, 30 and 40 years, for the sojourn with Germanus (it is to be observed that, of the two computations noticed above, one reckons with 30, the other with 40 years). If either of these, 30 years must have been the period accepted in this computation for St. Patrick’s studies, and an interval of 8 (or 7) years left, which agrees remarkably with the notice of Tírechán (from the Liber apud Ultanum, ib.): uii. aliis annis ambulauit, etc. The sum worked out thus—
22 + 7 + 30 + 61 = 120.
Of these items 22 had the best authority, and 30 and 7 were independent records or traditions (as we know from Muirchu and Tírechán). The problem is therefore reduced to discovering the origin of the 61 or 60 years during which the apostle is wrongly supposed to have taught. That it was due to a misinterpretation and not to a deliberate invention, there can, I think, be no question.
A list of the Armagh succession in the Book of Leinster (printed in Stokes, Trip. pp. 542 sqq.) supplies a hint which suggests an explanation of the error. The first entry is—
Patrick: 58 years from the coming of Patrick to Ireland till his death.